TooFewSignatories

The multisig signatory list is too short: other_signatories must contain at least one account besides the sender. Check the length of other_signatories against the threshold you are using.

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 TooFewSignatories.