It has been our experience that the issue you are reporting relates to an account issue that must be resolved by AWS customer service. I would suggest you look into options in the
AWS Account Management Portal, if accessible. Otherwise, follow up with options in recent confirmation email from AWS regarding your account.
There is another, similar AWS option now:
AWS Marketplace Wowza Standard, which works the same as devpay as far built-in licensing and no premium addon support. It is also a different AWS subscription involved. Note these are EBS backed instances, which means they can be stopped and re-started, whereas devpay S3 backed instances can only be terminated.