Sender '&1' is not registered with receiver &3(&2).

What causes this issue?

Sender system is not registered for remote connectivity on receiver
system. Therefore no communication through SOAManager Connectivity is
allowed.

System Response

Sender is not registered for remote connectivity in receiver system.

How to fix this error?

Please execute Connectivity Setup in transaction SOAMANAGER (Tab Remote
Connectivity) in system.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.