Registration failure over secure connection


Hello – We have Asterisk 13.26.0 with PJSIP and FreePBX. I am attempting to register a Yealink SIP-T40G phone over an encrypted connection.

We installed a Let’s Encrypt ceritificate in the asterisk using the FreePBX certificate manager. I followed the asterisk secure calling tutorial and made client certificates from the Let’s Encrypt certificate using the ast_tls_cert script and installed the appropriate files it in the Yealink phone.

When attempting to register the phone the connection is cut off by the Asterisk with a TCP FIN after the TLS handshake appears to complete. Here is the wireshark:

(the above packet capture was made with a weaker cipher suite so that the decrypted packets can be viewed. The same sequence of events occurs with the original strong cipher suite)

I went to Yealink support who only said I must look into why the server is disconnecting. Is there a way to enable enhanced CLI output to show why the Asterisk is cutting the connection?
When I turn up full verbose and debug on the Asterisk CLI I only get only the following information:

Any advice on this issue would be greatly appreciated.
Thank you!