app-ads.txt error The server URL could not be validated. Root domain URL

I am implementing ads for monetization and have filled out all the form. Last line asks for the developer URL.

Both the ads provider and I have double checked the URL, it works correctly and the app-ads.txt file displays in a browser, but when I enter the root domain URL, Roku form returns "The server URL could not be validated."

Any suggestions on how to fix this?

Thanks in advance.