message event modeling

Modeling a service waiting for a message event sent by a backend

Hello,
My question is very close to the question asked by Pierre Deville on the 04/16/2019: 'Send a message event via REST API' : how are you modeling a service waiting for a message event coming from a backend and not from an other process ?
My point is that if I use 'Receive task' or 'Catch message', those two steps require to specify the catch message from a drop-down list in General / General tab.
My understanding is that this drop-down list is populated with message declared in throw message steps. I am wrong ?

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