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FA-59586 / Subscription proration billing / Open access

Dunning retry schedule and status: retry offset base · case 01

Retries drift later with every failure.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Retry offsets are added to the failed attempt day instead of the invoice due date.

THE FAILURE

Retry offsets are added to the failed attempt day instead of the invoice due date.

Unsuccessful approach: The attempt accumulates offsets as if each were relative to the previous retry.

Case contract

Input {events: [[day, fail|pay]], due, retry: offsets from due for retries, final canceled|unpaid, today}. Events up to today are processed by day (stable). Payment settles: status active, no retry, stop. Each failure increments a counter; after more failures than scheduled retries the status becomes final and processing stops; otherwise past_due with next retry at due + retry[failures-1]. Return [status, next_retry].

Why this case matters

Payment retries drive subscription status; off-by-one retry counting cancels customers early or never.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    status = 'active'
    fails = 0
    nxt = None
    for day, kind in sorted(x['events'], key=lambda e: e[0]):
        if day > x['today']:
            break
        if status in ('canceled', 'unpaid'):
            break
        if kind == 'pay':
            status = 'active'; nxt = None; break
        fails += 1
        if fails > len(x['retry']):
            status = x['final']; nxt = None
        else:
            status = 'past_due'; nxt = day + x['retry'][fails - 1]
    return [status, nxt]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression', {'events': [[21, 'fail'], [8, 'fail'], [4, 'fail'], [23, 'fail']], 'due': 1, 'retry': [2, 4, 8, 16], 'final': 'canceled', 'today': 15}, ['past_due', 5]), ('regression', {'events': [[4, 'fail'], [11, 'fail']], 'due': 3, 'retry': [5], 'final': 'canceled', 'today': 8}, ['past_due', 8]), ('partial-repair probe', {'events': [[25, 'fail'], [22, 'fail']], 'due': 19, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 41}, ['past_due', 23]), ('partial-repair probe', {'events': [[15, 'fail'], [21, 'fail']], 'due': 8, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 31}, ['past_due', 12]), ('normal control', {'events': [], 'due': 2, 'retry': [5], 'final': 'unpaid', 'today': 4}, ['active', None]), ('normal control', {'events': [[19, 'fail'], [32, 'fail'], [37, 'fail'], [29, 'fail'], [33, 'pay'], [42, 'fail']], 'due': 19, 'retry': [3, 5, 7], 'final': 'canceled', 'today': 34}, ['active', None]), ('normal control', {'events': [[18, 'fail'], [12, 'fail'], [21, 'fail'], [19, 'fail']], 'due': 10, 'retry': [3, 5, 7], 'final': 'unpaid', 'today': 23}, ['unpaid', None]), ('normal control', {'events': [[24, 'pay'], [14, 'fail'], [13, 'pay'], [21, 'pay'], [16, 'fail'], [6, 'fail']], 'due': 5, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 35}, ['active', None])], [('regression', {'events': [[25, 'fail'], [22, 'fail']], 'due': 19, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 41}, ['past_due', 23]), ('regression', {'events': [[4, 'fail'], [11, 'fail']], 'due': 3, 'retry': [5], 'final': 'canceled', 'today': 8}, ['past_due', 8]), ('partial-repair probe', {'events': [[15, 'fail'], [21, 'fail']], 'due': 8, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 31}, ['past_due', 12]), ('partial-repair probe', {'events': [[25, 'fail'], [23, 'fail']], 'due': 2, 'retry': [1, 3], 'final': 'unpaid', 'today': 28}, ['past_due', 5]), ('normal control', {'events': [], 'due': 5, 'retry': [2, 4, 8, 16], 'final': 'canceled', 'today': 24}, ['active', None]), ('normal control', {'events': [[15, 'pay'], [8, 'pay'], [23, 'fail'], [23, 'fail']], 'due': 2, 'retry': [3, 5, 7], 'final': 'unpaid', 'today': 9}, ['active', None]), ('normal control', {'events': [[5, 'pay']], 'due': 3, 'retry': [1, 3], 'final': 'canceled', 'today': 18}, ['active', None]), ('normal control', {'events': [[17, 'fail'], [31, 'pay']], 'due': 8, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 16}, ['active', None])], [('regression', {'events': [[15, 'fail'], [21, 'fail']], 'due': 8, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 31}, ['past_due', 12]), ('regression', {'events': [[25, 'fail'], [22, 'fail']], 'due': 19, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 41}, ['past_due', 23]), ('partial-repair probe', {'events': [[20, 'fail'], [31, 'fail'], [11, 'fail']], 'due': 10, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 24}, ['past_due', 14]), ('partial-repair probe', {'events': [[16, 'fail'], [13, 'fail']], 'due': 0, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 23}, ['past_due', 4]), ('normal control', {'events': [[5, 'pay'], [15, 'fail']], 'due': 0, 'retry': [1, 3], 'final': 'unpaid', 'today': 2}, ['active', None]), ('normal control', {'events': [[15, 'fail']], 'due': 1, 'retry': [1, 3], 'final': 'canceled', 'today': 14}, ['active', None]), ('normal control', {'events': [], 'due': 13, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 26}, ['active', None]), ('normal control', {'events': [[22, 'fail'], [10, 'pay'], [11, 'fail'], [25, 'fail'], [15, 'fail'], [16, 'fail']], 'due': 10, 'retry': [1, 3], 'final': 'unpaid', 'today': 39}, ['active', None])], [('regression', {'events': [[25, 'fail'], [23, 'fail']], 'due': 2, 'retry': [1, 3], 'final': 'unpaid', 'today': 28}, ['past_due', 5]), ('regression', {'events': [[33, 'pay'], [13, 'fail']], 'due': 12, 'retry': [3, 5, 7], 'final': 'canceled', 'today': 22}, ['past_due', 15]), ('partial-repair probe', {'events': [[28, 'fail'], [26, 'fail']], 'due': 13, 'retry': [1, 3], 'final': 'canceled', 'today': 38}, ['past_due', 16]), ('partial-repair probe', {'events': [[28, 'fail'], [27, 'fail'], [40, 'fail']], 'due': 16, 'retry': [3, 5, 7], 'final': 'canceled', 'today': 33}, ['past_due', 21]), ('normal control', {'events': [[21, 'fail'], [22, 'pay'], [30, 'fail'], [27, 'fail']], 'due': 16, 'retry': [5], 'final': 'canceled', 'today': 32}, ['active', None]), ('normal control', {'events': [[28, 'fail']], 'due': 17, 'retry': [1, 3], 'final': 'unpaid', 'today': 21}, ['active', None]), ('normal control', {'events': [[27, 'pay'], [21, 'fail'], [28, 'fail'], [31, 'fail'], [19, 'pay'], [21, 'fail']], 'due': 15, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 39}, ['active', None]), ('normal control', {'events': [], 'due': 1, 'retry': [2, 4, 8, 16], 'final': 'canceled', 'today': 30}, ['active', None])], [('regression', {'events': [[20, 'fail'], [31, 'fail'], [11, 'fail']], 'due': 10, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 24}, ['past_due', 14]), ('regression', {'events': [[15, 'fail'], [21, 'fail']], 'due': 8, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 31}, ['past_due', 12]), ('partial-repair probe', {'events': [[24, 'fail'], [30, 'fail']], 'due': 15, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 38}, ['past_due', 19]), ('partial-repair probe', {'events': [[34, 'fail'], [14, 'fail']], 'due': 11, 'retry': [3, 5, 7], 'final': 'canceled', 'today': 35}, ['past_due', 16]), ('normal control', {'events': [[8, 'fail'], [9, 'fail'], [33, 'pay']], 'due': 8, 'retry': [3, 5, 7], 'final': 'unpaid', 'today': 8}, ['past_due', 11]), ('normal control', {'events': [[20, 'fail'], [17, 'fail'], [24, 'pay'], [6, 'pay'], [7, 'fail'], [27, 'fail']], 'due': 3, 'retry': [1, 3], 'final': 'canceled', 'today': 16}, ['active', None]), ('normal control', {'events': [[18, 'pay'], [16, 'fail'], [28, 'fail'], [22, 'fail']], 'due': 7, 'retry': [1, 3], 'final': 'unpaid', 'today': 37}, ['active', None]), ('normal control', {'events': [[21, 'fail'], [30, 'fail'], [22, 'fail']], 'due': 15, 'retry': [5], 'final': 'canceled', 'today': 37}, ['canceled', None])]]
for i, (label, args, expected) in enumerate(fixtures[N-1]):
    check("%s %d" % (label, i), solve(args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression 0['past_due', 12]['past_due', 5]Failed
regression 1['past_due', 9]['past_due', 8]Failed
partial-repair probe 2['past_due', 29]['past_due', 23]Failed
partial-repair probe 3['past_due', 25]['past_due', 12]Failed
normal control 4['active', None]['active', None]Passed
normal control 5['active', None]['active', None]Passed
normal control 6['unpaid', None]['unpaid', None]Passed
normal control 7['active', None]['active', None]Passed

SHA-256 / 0ed361668c74eb3ee934030ff108c09c72458dae350890ee8cc0549f63b946d1

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    status = 'active'
    fails = 0
    nxt = None
    for day, kind in sorted(x['events'], key=lambda e: e[0]):
        if day > x['today']:
            break
        if status in ('canceled', 'unpaid'):
            break
        if kind == 'pay':
            status = 'active'; nxt = None; break
        fails += 1
        if fails > len(x['retry']):
            status = x['final']; nxt = None
        else:
            status = 'past_due'; nxt = x['due'] + sum(x['retry'][:fails])
    return [status, nxt]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression', {'events': [[21, 'fail'], [8, 'fail'], [4, 'fail'], [23, 'fail']], 'due': 1, 'retry': [2, 4, 8, 16], 'final': 'canceled', 'today': 15}, ['past_due', 5]), ('regression', {'events': [[4, 'fail'], [11, 'fail']], 'due': 3, 'retry': [5], 'final': 'canceled', 'today': 8}, ['past_due', 8]), ('partial-repair probe', {'events': [[25, 'fail'], [22, 'fail']], 'due': 19, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 41}, ['past_due', 23]), ('partial-repair probe', {'events': [[15, 'fail'], [21, 'fail']], 'due': 8, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 31}, ['past_due', 12]), ('normal control', {'events': [], 'due': 2, 'retry': [5], 'final': 'unpaid', 'today': 4}, ['active', None]), ('normal control', {'events': [[19, 'fail'], [32, 'fail'], [37, 'fail'], [29, 'fail'], [33, 'pay'], [42, 'fail']], 'due': 19, 'retry': [3, 5, 7], 'final': 'canceled', 'today': 34}, ['active', None]), ('normal control', {'events': [[18, 'fail'], [12, 'fail'], [21, 'fail'], [19, 'fail']], 'due': 10, 'retry': [3, 5, 7], 'final': 'unpaid', 'today': 23}, ['unpaid', None]), ('normal control', {'events': [[24, 'pay'], [14, 'fail'], [13, 'pay'], [21, 'pay'], [16, 'fail'], [6, 'fail']], 'due': 5, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 35}, ['active', None])], [('regression', {'events': [[25, 'fail'], [22, 'fail']], 'due': 19, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 41}, ['past_due', 23]), ('regression', {'events': [[4, 'fail'], [11, 'fail']], 'due': 3, 'retry': [5], 'final': 'canceled', 'today': 8}, ['past_due', 8]), ('partial-repair probe', {'events': [[15, 'fail'], [21, 'fail']], 'due': 8, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 31}, ['past_due', 12]), ('partial-repair probe', {'events': [[25, 'fail'], [23, 'fail']], 'due': 2, 'retry': [1, 3], 'final': 'unpaid', 'today': 28}, ['past_due', 5]), ('normal control', {'events': [], 'due': 5, 'retry': [2, 4, 8, 16], 'final': 'canceled', 'today': 24}, ['active', None]), ('normal control', {'events': [[15, 'pay'], [8, 'pay'], [23, 'fail'], [23, 'fail']], 'due': 2, 'retry': [3, 5, 7], 'final': 'unpaid', 'today': 9}, ['active', None]), ('normal control', {'events': [[5, 'pay']], 'due': 3, 'retry': [1, 3], 'final': 'canceled', 'today': 18}, ['active', None]), ('normal control', {'events': [[17, 'fail'], [31, 'pay']], 'due': 8, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 16}, ['active', None])], [('regression', {'events': [[15, 'fail'], [21, 'fail']], 'due': 8, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 31}, ['past_due', 12]), ('regression', {'events': [[25, 'fail'], [22, 'fail']], 'due': 19, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 41}, ['past_due', 23]), ('partial-repair probe', {'events': [[20, 'fail'], [31, 'fail'], [11, 'fail']], 'due': 10, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 24}, ['past_due', 14]), ('partial-repair probe', {'events': [[16, 'fail'], [13, 'fail']], 'due': 0, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 23}, ['past_due', 4]), ('normal control', {'events': [[5, 'pay'], [15, 'fail']], 'due': 0, 'retry': [1, 3], 'final': 'unpaid', 'today': 2}, ['active', None]), ('normal control', {'events': [[15, 'fail']], 'due': 1, 'retry': [1, 3], 'final': 'canceled', 'today': 14}, ['active', None]), ('normal control', {'events': [], 'due': 13, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 26}, ['active', None]), ('normal control', {'events': [[22, 'fail'], [10, 'pay'], [11, 'fail'], [25, 'fail'], [15, 'fail'], [16, 'fail']], 'due': 10, 'retry': [1, 3], 'final': 'unpaid', 'today': 39}, ['active', None])], [('regression', {'events': [[25, 'fail'], [23, 'fail']], 'due': 2, 'retry': [1, 3], 'final': 'unpaid', 'today': 28}, ['past_due', 5]), ('regression', {'events': [[33, 'pay'], [13, 'fail']], 'due': 12, 'retry': [3, 5, 7], 'final': 'canceled', 'today': 22}, ['past_due', 15]), ('partial-repair probe', {'events': [[28, 'fail'], [26, 'fail']], 'due': 13, 'retry': [1, 3], 'final': 'canceled', 'today': 38}, ['past_due', 16]), ('partial-repair probe', {'events': [[28, 'fail'], [27, 'fail'], [40, 'fail']], 'due': 16, 'retry': [3, 5, 7], 'final': 'canceled', 'today': 33}, ['past_due', 21]), ('normal control', {'events': [[21, 'fail'], [22, 'pay'], [30, 'fail'], [27, 'fail']], 'due': 16, 'retry': [5], 'final': 'canceled', 'today': 32}, ['active', None]), ('normal control', {'events': [[28, 'fail']], 'due': 17, 'retry': [1, 3], 'final': 'unpaid', 'today': 21}, ['active', None]), ('normal control', {'events': [[27, 'pay'], [21, 'fail'], [28, 'fail'], [31, 'fail'], [19, 'pay'], [21, 'fail']], 'due': 15, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 39}, ['active', None]), ('normal control', {'events': [], 'due': 1, 'retry': [2, 4, 8, 16], 'final': 'canceled', 'today': 30}, ['active', None])], [('regression', {'events': [[20, 'fail'], [31, 'fail'], [11, 'fail']], 'due': 10, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 24}, ['past_due', 14]), ('regression', {'events': [[15, 'fail'], [21, 'fail']], 'due': 8, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 31}, ['past_due', 12]), ('partial-repair probe', {'events': [[24, 'fail'], [30, 'fail']], 'due': 15, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 38}, ['past_due', 19]), ('partial-repair probe', {'events': [[34, 'fail'], [14, 'fail']], 'due': 11, 'retry': [3, 5, 7], 'final': 'canceled', 'today': 35}, ['past_due', 16]), ('normal control', {'events': [[8, 'fail'], [9, 'fail'], [33, 'pay']], 'due': 8, 'retry': [3, 5, 7], 'final': 'unpaid', 'today': 8}, ['past_due', 11]), ('normal control', {'events': [[20, 'fail'], [17, 'fail'], [24, 'pay'], [6, 'pay'], [7, 'fail'], [27, 'fail']], 'due': 3, 'retry': [1, 3], 'final': 'canceled', 'today': 16}, ['active', None]), ('normal control', {'events': [[18, 'pay'], [16, 'fail'], [28, 'fail'], [22, 'fail']], 'due': 7, 'retry': [1, 3], 'final': 'unpaid', 'today': 37}, ['active', None]), ('normal control', {'events': [[21, 'fail'], [30, 'fail'], [22, 'fail']], 'due': 15, 'retry': [5], 'final': 'canceled', 'today': 37}, ['canceled', None])]]
for i, (label, args, expected) in enumerate(fixtures[N-1]):
    check("%s %d" % (label, i), solve(args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression 0['past_due', 7]['past_due', 5]Failed
regression 1['past_due', 8]['past_due', 8]Passed
partial-repair probe 2['past_due', 25]['past_due', 23]Failed
partial-repair probe 3['past_due', 14]['past_due', 12]Failed
normal control 4['active', None]['active', None]Passed
normal control 5['active', None]['active', None]Passed
normal control 6['unpaid', None]['unpaid', None]Passed
normal control 7['active', None]['active', None]Passed

SHA-256 / a8604ed048765f913cc98a1687cf78ff487784f4b15a3951de3518cf9d7a0bee

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 8 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

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Verification & scope

A deterministic teaching model of a stipulated billing rule. It makes no claim to reproduce any billing provider's exact behaviour and is not billing software. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:46:37.682783+00:00.

Case digest / 111f13927821170ecab1da479c086d4288037396f307d628aa901d59655d91bd