Swap refunds only handle last output

[michael1011]

There are cases in which user send more than one transaction to the swap address. That causes some the issue that in the extension, if the swap fails, only the last output is refunded when all of them should be refunded.

Also that if the swap succeeds, all unspent outputs should also be refunded

[BenGWeeks]

Good news! According to Claude Code this issue appears to be resolved in Boltz API v2, which uses cooperative refunds with partial signatures (MuSig2).

The Boltz team already implemented multi-UTXO refunds in their web app:

• Issue: Refund all UTXOs in one transaction BoltzExchange/boltz-web-app#855 - "Refund all UTXOs in one transaction" (P0 priority)
• Implementation: feat: Refund all UTXOs in one transaction BoltzExchange/boltz-web-app#864 - Released in v1.7.1 (March 2025)

In API v2, clients can construct refund transactions with multiple inputs (all UTXOs sent to the swap address), request Boltz's partial signature via POST /swap/submarine/{id}/refund, then aggregate and broadcast. This handles the scenario where users send multiple transactions to the same swap address.

@dni - I believe you're working on migrating the LNbits extension to API v2, which should automatically resolve this issue once implemented.