SenderInSignatories

The multisig sender was included in the other_signatories list, but that list must contain only the remaining signatories. Remove the sender's own account from other_signatories before resubmitting.

Declared by the Multisig pallet; it classifies to the semantic code invalid_argument.

Remediation

Check the argument values against the operation schema

The same explanation is available in the terminal: btcli explain SenderInSignatories.