Due to an issue with the security of the TLS certificate used by Snom DECT, many of the older hardware versions are no longer supported in Auto Provisioning. The issue is that the old SHA1 certificates used are vulnerable to attacks and therefore our servers reject it.
This includes the M300, M700 Series of devices and a select range of M900 DECT devices.
It was confirmed to us by Snom support, that these SHA1 certificates cannot be replaced manually either.
With Snom M900 DECT, there are different hardware versions in circulation. The first generation hardware version R1A is affected. All newer hardware versions, R1B and can provision without issues.
You can see the hardware version on the back of the device, like described in this article by Snom.