Can't use custom phone templates on SP4

[advanced25]

We are deploying our first customer on SP4 and we're finding that when using a custom phone template, the phones will not provision. The proof:

1. Setup an extension to use the Yealink standard template
2. Go to the provisioning URL / PHONE-MAC.cfg and the XML file is downloaded
3. Copy the standard Yealink template and make no changes.
4. Setup an extension to use the copied template
5. Go to the provisioning URL / PHONE-MAC.cfg and the XML file is not found
   
6. Change back to the standard template and the XML file is downloadable again.

Any thoughts on what's going on here?

 

[Saqqara]

Check out playing attention to the Yealink extra steps - https://www.3cx.com/docs/custom-ip-phone-templates/