Subdomain - Redirecting and unmask/mask

Subcategory - Redirecting Subdomain

Hi All,
I have created a subdomain and am redirecting it to my knack URL: I did this by adding it to my domain’s DNS.

It works perfectly, so the user can type in and it redirects them to Online Database Software: Create a No Code Database | Knack. Now, when I created it I kept it as Unmasked. However, if I change it to Masked (so that the URL says instead of the Knack URL, the https fails. I am assuming it is failing because Knack doesn’t have a certificate for my subdomain name.

Knack supports says they cannot comment as it is outside their support, but wanted to check with others to see if anyone else has addressed this, and in what way.

The other option I see is that I can create a separate website page for each customer under my website/domain and embed my home page code for each application (customer), so my URL would be handled from my website (e.g.**xyz**)

I hope I didn’t make it more confusing than it needs to be. Thanks for your help in advance.