Invalid signature when transaction.feePayer set with external account

[mikestead]

Summary

When transaction.feePayer is set with an address that is not managed by Phantom, Phantom appears to sign the transaction as the fee payer, causing a mismatch between transaction.signatures[0].publicKey transaction.signatures[0].signature. Where the first signature in this array is always the fee payer (from my understanding).

Example

No response

Steps to Reproduce

1. Create a basic tx with a transfer and set the tx.feePayer to an account other than the one managed by Phantom
2. Pass the transaction to Phantom for signing
3. Inspect tx.signatures[0].publicKey, it will equal our original tx.feePayer
4. Inspect tx.signatures[0].signature, it will exist and must have been signed by phantom with different pubkey

Expected

Phantom should not assume it's signing as fee payer if transaction.feePayer is set with a different pubkey to the one it's signing with.

Context

This relates multi-sig and trying to find a solution for https://github.com/orgs/phantom/discussions/122

Phantom Version

23.17.0

Is there an existing discussion for this?

• I have searched the existing discussions