3300 returns an ICMP Destination Unreachable (port unrechable)

[handwritten]

We have a 3300 with a SIP trunk to an Audiocodes Mediant SBC. We use this for a Teams Direct Routing implementation. We can call from the 3300 to Teams via the SBC, but not the other way around. Calls are dropped, and the 3300 returns an ICMP error. We double checked the port and protocol (UDP 5062) as set up in the Network Elements form on the 3300. Any clues?

[Dogbreath]

5062 is not the normal SIP listening port so have you changed this on the 3300?

[handwritten]

I had set this back to 5060 and this seems to help. However, I'm getting a 488 'not acceptable here' error from the SBC. I took a look at the SIP ladder, and indeed the 3300 is not specifying any codecs. Here's the relevant section in the 183 message:

v=0
o=- 2049 2049 IN IP4 [redacted IP]
s=-
c=IN IP4 [redacted IP]
t=0 0
m=audio 0 RTP/SAVP 18

In a working SIP exchange, the host responds with proposed codecs. Not the case here.

[NEPhoneGuy]

The invite is coming from teams right? Share a pcap of the entire exchange. Feel free to PM if you don't want to share. Curious what teams is offering in the initial invite.