For projects using credit card billing, the billing contact is automatically set to the user who owns the project's credit card. This means that it is assigned to the user who added the payment card and assigned the project(s) to it. The billing contact cannot be removed from the project.
In order to change the billing contact user, a new payment card must be added in the account of the user we want the billing contact to be assigned to. The new payment card can be the same one being used at the moment.
Add a new payment card
Go to the User profile by clicking on the User information icon on the top right of the screen.
Then click the Payment Options tab.
Add the new credit card details and Save card.
In the new card added, assign the project(s) from the previous card by clicking on assign to project.
Once the project(s) have been assigned, the billing contact has been changed and also the previous billing contact user can be deleted if needed.