Bar tab system: authorize $40 when the card is opened, capture the final total with tip when the tab closes. Worked fine until a night with heavy tipping pushed captures 25-30% over the original authorization.
Turns out card networks cap how much a capture can exceed the initial auth without a step-up. Visa's tolerance for restaurant MCC 5812 is 20% over the authorized amount. Go past that and the issuer can decline the capture outright, or your gateway silently splits it into a new incremental authorization request that gets evaluated independently, with its own risk scoring, its own chance of a soft decline unrelated to the original approval.
The threshold isn't universal either. Lodging and car rental MCCs get different tolerance rules because no-shows and extended stays are expected to run over. Retail MCCs generally get none, an exact-match capture or nothing.
Our capture code just sent whatever the final total was and let the processor sort it out. It sorted it out by declining roughly 1 in 30 tabs over $100, all clustered on nights with above-average tip percentages. Fix was capping tip-adjusted captures at 18% over auth and forcing a fresh authorization for anything beyond that.
Anyone tracking these tolerance percentages per network/MCC combo, or is everyone just hardcoding one number and hoping?
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