You can save the prompts in μ-Law or A-Law. While saving a prompt file, ensure that the 8.000 kHz, 8 Bit, Mono 7 kb/sec attribute is selected. (https://<FQDN of UCCX>/appadmin/help/default/appadmin/help/output/index.html#!uccx_r_125record-prompt.html...

CE9.9.0/CE9.8.1 and below – Recommended upgrade path for Webex Room Systemsfound on page 24 of this link: https://www.cisco.com/c/dam/en/us/td/docs/telepresence/endpoint/software/ce9/release-notes/ce-software-release-notes-ce9.pdf

Cisco TAC sent me this link that might be helpful. https://video.cisco.com/detail/video/6274513704001However, my Webex room kit was on OS: version=ce10.8.3.1 6d131e0418f 2021-12-06We downgraded to version CE9.15.6 StepUpgrade then upgraded to 10.19. ...

You may have to upgrade the software on the room kit.  I had this same problem and there was another software upgrade that Cisco TAC provided which I had to install before even getting to the final upgraded version.

SEP stands for Selsius Ethernet Phone, which was the original company that created Call Manager.  Cisco later acquired this company but the SEP from the original company was retained.