No connection to SAP gateway (TXCOM destination &); see SAP system log

What causes this issue?

No connection could be made to the SAP gateway with TXCOM destination
&v1&.

How to fix this error?

Check the gateway and supply the TXCOM with the correct values where
necessary.
The sending of this IDoc will be restarted automatically as long as the
maximum repeat count is not exceeded.

Error message extract from SAP system. Copyright SAP SE.