More than one interface is assigned to class &1 &2

What causes this issue?

An interface in the SAP Application Interface Framework could not be
determined for this message due to one of the following reasons:
For the proxy class &1, more than one interface has been assigned (not
only different versions, but different interface names).
The interface determination (based on Customizing for the SAP
Application Interface Framework under <DS:SIMG./AIF/INFDETP>Interface
Determination for Proxy Interfaces</>) did not find the interface in the
SAP Application Interface Framework, probably because the data contained
an unexpected value.

System Response

In a scenario where the Proxy message is to be processed in AIF, the
system sets the message to an error status (<ZK>Application Error </>)
because it could not be processed.
In a scenario where the Proxy message processing is only to be monitored
in AIF, there is just this error message written to the application log
for your information. Because the Proxy message might not be in the
monitoring scope by intention.

How to fix this error?

Check which fields should determine the interface. You may then do one
of the following:
Change the Customizing in <DS:SIMG./AIF/INFDETP>Interface Determination
for Proxy Interfaces</> and restart the message if in an error status.
Cancel the message and send it again from the sending system (if the
data is wrong).

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.