Scope

I am getting "Upgrade to a higher plan to use this API. Please contact [email protected]" error while updating payment method of a customer.

Summary

This solution article covers the reason and steps to resolve the "Upgrade to higher plan to use this API. Please contact [email protected]" error while updating the payment method of a customer using the API. 

Solution
This error occurs when your site is below the scale plan and you are trying to add multiple cards to a customer, which is not possible.  It's a feature restriction.

In order to fix this error, you can pass the "replace_primary_payment_source" as "true"(link) with your API call. 

This would ensure the existing payment method is replaced with the one newly passed via the API call.

Related articles and Documentation
Payment Sources API