CASCS1015E Outbound transaction routing of transaction trans-id failed because system 'system-id' is not acquired.

Problem:

CASCS1015E Outbound transaction routing of transaction trans-id failed because system 'system-id' is not acquired. 

Documentation references here.

Resolution:

If this error is encountered after a successful CRTE transaction in an MSS CICS to MSS CICS setup, then it may be caused by
a) the name of the ISC listener - give it a 4-char name, something like ‘ISC1’
b) a missing ephemeral port on the ISC listener in the Originating MSS Region

Example ISC definition in originating region: