When I try to delete a User ID, there is an error prompted ‘Unable to delete the record because it has been referenced by IV.’?
It is due to the User ID has been used to create transactions in Invoice thus unable to delete.
You may inactive the User ID.
1) Go to Account Book Icon > User, click on Edit on the USER ID that you wish to inactive.
2) Go to ‘Account’ tab, click on ‘Remove Link’ for the email and Save.
The user is Inactive now.