@Patrick Pouw Thanks for reaching out to Microsoft Q&A.
As per documentation, the reason for the error that you are receiving is-
CannotParseValidCertificateFromRIRPage - Can't parse the public key for the IP prefix using the registration data access protocol (RDAP) of the regional internet registry (RIR).
I understand that you have already verified that the config is correct, however, since the error message indicates that there is a parsing issue, I would re-check the steps and confirm that the Public Key for the IP Prefix is correct.
Please go through the steps, especially. the Certificate Readiness. If this does not help, please reach out to Azure Support directly to verify the issue. Hope this helps.
Please let us know if you have any more questions and we will be glad to assist you further. Thank you!
Remember:
Please accept an answer if correct. Original posters help the community find answers faster by identifying the correct answer. Here is [how][1].
Want a reminder to come back and check responses? Here is [how][2] to subscribe to a notification.