Notification(s) of type &1 with version &2 from provider &3 is ignored

What causes this issue?

Ignoring the notification for OData flows where Is_Groupable is marked
as undefined, as the gateway runtime raises an exception for undefined
Boolean type.

System Response

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

How to fix this error?

Notification Provider needs to pass the Is_Groupable flag present in
exporting parameter ES_NOTIFICATION_TYPE from the method
/IWNGW/IF_NOTIF_PROVIDER~GET_NOTIFICATION_TYPE of the provider class.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.