If you have configured your custom Clippings.me domain as 'www.yourname.com', the address entered needs to have the 'www' - it won't work if you drop that part and only enter the naked/APEX domain (i.e. yourname.com).
Confusingly, some browsers will automatically append the 'www' if you forget to enter it, leading to inconsistent behavior between visitors.
The easiest way to fix this is see if your domain registrar offers an offer to forward your naked/APEX domain to your full url (that includes the 'www'). Most registrars offer this but not all do so we have a backup option.
1) You'll need to go back to your DNS setting pages with your domain registrar and to the same area you setup your original CNAME.
This time instead of setting up a CNAME we'll be setting up an 'A' (browse the options of what they allow you to setup and you should see it).
2) For the name/host put '@' (without the quotes).
3) For the value put '18.104.22.168' (without the quotes).
4) We need to add another line just like you did with the 'A' in step 1, however now you need to select 'TXT'.
5) For the name/host put '@' (without the quotes).
6) For the value put 'apex=secured.clippings.me' (without quotes).
7) Please try going directly to https://yourdomain.com now. You should see a security error, this will start the process of setting it up and if you hit reload about 5 minutes later it should be working.
If you have any issues, please submit a ticket and include screenshots of your DNS settings page if possible.