M…) is an ed25519 account plus a 64-bit ID. Exchanges and custodians use the ID to tell their customers apart inside one Stellar account.
The rules
- Index balances on the underlying
G…account. The ledger has no muxed accounts. Balances live on the base account. - Keep the ID with the record, exactly (see 64-bit integers). wallet-backend stores it as
to_muxed_idTEXT. - Expect fee-bumps. Muxed destinations often arrive wrapped in a fee-bump, as in
cap27-muxed-payment-pubnet-0001, so the operation is atfeeBump.tx.innerTx.v1.tx.operations[i]. Code that only handlesv1envelopes skips them. - Round-trip the
M…strkey through your SDK in tests. All three SDKs pass on this fixture.