If the issue still persists, you can fill out this form from the Google Cloud Billing team to help with your issue, as you are getting an error message when attempting to make a payment. State the issue that you are experiencing and the error code. Please remember also to not provide any identifying information or sensitive financial information like credit card numbers.
Additionally, I recommend reaching out to the Cloud Billing team as they have the right resources that might be more helpful in resolving your Cloud Billing related issues.
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