Per this article, you can only add a tip up to 36 hours after the transaction has been settled. After that, the transaction is settled with a $0 tip. Here's the relevant portion of the article:
Settle Payments in the Square App
After you’ve completed a payment with a signed receipt, you can settle the transaction and record the final payment amount. You have 36 hours to add a tip and settle the transaction. There are two options for settling your payments:
- Add tips and settle transactions individually
- Bulk settle multiple transactions
After 36 hours, all unsettled payments will be automatically settled with a $0 tip. After a payment has been settled, the tip amount can’t be adjusted. Settled sign and tip payments will be included in your next transfer following your transferschedule. They’ll also appear as completed in your in-app and online sales history and will be included in your Transactions CSV.
Judy T Shumway
