Hi,
in the Page “Challenge” there is a computed field with this formula:

Key:=@UrlQueryString( “Key” );
Host:=@Trim(@UpperCase(@GetHTTPHeader(“Host”)));
Value:=@DbLookup(“Notes”:“NoCache”;““:““;“(LookupDomain)“;Host;2);
@If(@IsError(Value);“ERROR: No value for domain found: " + Host;Key + “.” +Value)

According to this the problem is that the lookup cant find any document in the hidden view “(LookupDomain)” for the entry “NOTES.COMPANYDOMAIN.COM”.
You should check the view and see if you can spot why the lookup is failing.
Maybe you have an additional space in the domain name (at the beginning or the end)? " NOTES.COMPANYDOMAIN.COM”

Sorry i did not have the time to do a polished app, so its more of a prototype.

But maybe you want to look here as well: https://www.midpoints.de/LE4D
(Its free but not opensource. And i am in no way affiliated with this project)

Bye
Hynek