Hey Vapi team, we're facing a critical integration issue and need your technical guidance. Objective: Our SIP trunk provider requires us to limit the offered codecs to

PCMA

,

PCMU

, and

G729

to mitigate a high percentage of connection failures (

503

,

403

errors). Problem: We're trying to update our BYO SIP Trunk credential to set these codec preferences. Based on documentation, we attempted to use the

codecPreferences

field. However, the API rejects the request. API Request Sent: - Method:

PATCH

- Endpoint:

https://api.vapi.ai/credential/da9a3dfc-d738-4c21-ab20-ec18725aeba0

- Body:

json
  {
    "codecPreferences": [
      "PCMA",
      "PCMU",
      "G729"
    ]
  }

API Response Received: - Status Code:

400 Bad Request

- Body:

json
  {"message":["property codecPreferences should not exist"],"error":"Bad Request","statusCode":400}

Question: Could you please provide the correct and currently supported method for setting a prioritized list of audio codecs on a

byo-sip-trunk

credential via the API? This is a major blocker for our production scaling, and any precise technical help would be greatly appreciated. Thank you!

cc: @kyle

@Gerónimo For codec control with BYO SIP trunks, configure codec preferences at your SIP trunk provider level rather than through Vapi's configuration. This gives you the most control over: -Codec selection and priority -Bandwidth management -Quality settings -Fallback options Your SIP trunk provider's codec configuration will be respected during the SIP negotiation process with Vapi's infrastructure. The only codec we don't accept and will actively block is G.729 but everything else should pass through