Internet Transaction Server not available

What causes this issue?

No connection to the Internet Transaction Server could be established.
Either output processing was not accessed from the Internet browser, or
there is temporarily no connection to the Internet Transaction Server.

System Response

Output processing is canceled and the status is set to "Incorrectly
processed".

How to fix this error?

Try again later to process the output from the Internet.

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.