To remove an invoice reference on the Client Card, head over to the Client Card, Details-view, under the Payer section.
To remove the Invoice Reference, click on the 'X'-icon () that is on the far right of the field.
Once you have removed an invoice reference, it will appear as below.
1. Ensure that you are either a Client Manager, a user with 'Assistant'-role, or 'Administrator'-rights to be able to remove an Invoice Reference.