Have you sorted this out? Because I have similar situation when submitting documents for parents. After so many confusion on what to do. I got a notary from a lawyer and had my parents get an affidavit of marriage from federal high court Lagos. When uploading documents, don’t click on available documents but rather click on the option that says document not available. Afterwards upload the affidavit and notary to the other documents section and leave a comment explaining why you can’t provide a marriage certificate. In my case , my parents had both traditional and church wedding but no court wedding and they have been married for 40 years. Let me know if you require further clarification on this. Good luck.