You are trying to install an add-on to an app but are getting denied.
First, make sure that the app you are working with is owned by you. If you only have
Collaborator access to it, it doesn't matter if your Personal account has a verified credit card. Only the app owner can provision add-ons, so they have to have a valid credit card entered in their own billing page for verification.
See this help page for more information:
If you are the owner and are encountering issues anyway, please open a support ticket for assistance. Be sure to indicate the name of the app affected, the contents or details of the error message, and anything else that might help diagnose the problem.