In the documentation for
initiateTransfer, it says that a bundle containing a multisig transfer can only have one input (emphasis mine):
Initiates the creation of a new transfer by generating an empty bundle with the correct number of bundle entries to be later used for the signing process. It should be noted that currently, only a single input (via inputAddress) is possible. The remainderAddress also has to be provided and should be generated by the co-signers of the multi-signature before initiating the transfer.
Why is only one input allowed? Is this a limitation of multisig?