It's likely protesting because of "Microsoft" in your subdomain, try removing/replacing this part just for the sake of testing. On my end, I am able to add this:
https://cbv-ms-sync-auth.naya-app.com/integrations/microsoft/oauth/redirect
but not this:
https://cbv-microsfot-sync-auth.naya-app.com/integrations/microsoft/oauth/redirect
Or you can open a support ticket to see if they can whitelist your URI.