As reported on the blog[1] (don’t forget to check it out in general - it’s a great resource!):
If you are a user of the DPMA module for Asterisk with Sangoma D-series phones, then this announcement is for you.
The D-Series phones have an upcoming expiration (May 28th, 2021) on the SSL certificate used when connected to certain versions of Asterisk, FreePBX, and PBXact systems. Sangoma has developed quick to implement and future proof solutions below.
These fixes will require administrator action before May 28th, 2021.
Further information including fixed versions and instructions are available on the Asterisk wiki here.
[1] Urgent: DPMA SSL Announcement ⋆ Open Source Communications Software | Asterisk Official Site