After applying the 7.8.0 update, and attempting to enter a new credit card on a client via the admin area, the following error is displayed:

An error occurred while communicating with the server. Please try again.

Additional logic is required to handle this scenario.

Add the card through the client area via the My Billing >  Payment Methods page. This may require 3D Secure acceptance by a client  depending on the card being added.              

A hotfix has been created which will resolve this error by  including  additional logic to handle this scenario. It can be  downloaded from:

https://whmcs.community/files/file/108-module-7096-%09-an-error-occurred-while-communicating-with-the-server-adding-a-card-via-the-admin-area-with-stripe/

Once the hotfix is applied, remote cards can be successfully added via the admin area