Microsoft 356 Add on: office 365 has been configured to prevent individual acquisition and execution of Office Store Add-ins

Question

Hey,

One of my clients want's to use visio as an add on for Excel.
I followed the steps previously stated in this post: https://answers.microsoft.com/en-us/msoffice/forum/all/office-365-has-been-configured-to-prevent/f1c94398-b570-4076-8099-f6f16e75965c
But it still keeps giving the same error for my client?

Is there anybody with a solution?

Kind Regards
Neil Ledoux