IDoc interface is not complete for message type ...

Hi Expert;

I try to put in place the creation of a reservation via an inbound IDoc type MRESCR. I did the Setup and I'm being testing.

I created an Idoc via WE19. The Idoc is visible in the BD87, however, I have an error message which I can't resolve. The message is this. 

The IDoc interface is not complete for message type ZMRESCR

Message no. B1500

I again checked my customizing and I can't locate the source of error. 

Can you guide me, with your advice, so that I can correct this anomaly.

Thanks in advance to all.