Hello
@Alex@kh,
We would like to inform you that you are getting this error as your SSL is not correctly added so we will suggest you to add SSL again, once you add the SSL on your custom domain then you will not get the Invalid URL error.
Since, for a custom domain SSL, we only support Cloudflare DNS. Your DNS should be on Cloudflare for us to SSL your custom domain.
All other SSL requests can’t be accepted.
Tutorial guide :
With the custom domain feature, you'll have your own customized checkout page. So, you can add your own domain name which will appear on the checkout page.
www.pabbly.com
Video tutorial for Cloudflare DNS :
If you still face the same issue, please feel free to reach us.
Regards,
Vipin Mishra