User not receiving notification either by email or bell notification

Summary

User not receiving notification either by email or bell notification that an invoice has been approved but receives them both if an Expenses Report is submitted

Content

User not receiving notification either by email or bell notification that an invoice has been approved but receives them both if an Expenses Report is submitted

User not receiving notification either by email or bell notification that a manual invoice he raises has been approved. These are showing in his Worklist, but the user wants to be able to have a visual notification that they have been approved. I have tested this in DEV-EDZZ-TEST and replicated that this does not happen however, if the same user raises an expense report and this is approved, he receives both bell notification and email confirming the approval.I am unable to find the reason why these are not been notified.