409
fees.proposal_pendingfeesRule R13This merchant already has a proposal awaiting a decision
One open proposal at a time, so a merchant is never asked to choose between two pricing offers that both claim to be current.
Why the API refuses
WHEN ProposeAssignment is executed while the tenant already has an assignment in status proposed, THE SYSTEM SHALL reject it.
What to do
Let the merchant accept or decline the open proposal, or withdraw it, before proposing another.