3.5.5.2.1.3 Receiving a TXUSER_PHASE0_MTAG_PHASE0REQ Message
When the resource manager receives a TXUSER_PHASE0_MTAG_PHASE0REQ message, the resource manager MUST perform the following actions:
If the connection state is Active:
Set the connection state to Processing Phase Zero Request.
Send a Phase Zero request to the higher-layer business logic so that the resource manager can receive the Phase Zero outcome from the higher-layer business logic via the Phase Zero Request Completed (section 3.5.4.8) event.
Otherwise, the message MUST be processed as an invalid message as specified in section 3.1.6.