Hi Support Team, We're experiencing critical issues when using Telnyx-registered phone numbers for VAPI-initiated outbound calls. The same assistant configuration works perfectly with Twilio-registered numbers, suggesting a provider-specific integration issue. Issue Summary Symptoms: 1. 15-second delay before AI agent starts speaking after call connects 2. AI hallucination - Stuck in between, repeat some of the sentences, etc. 3. Poor voice activity detection - AI doesn't recognize when customer speaks as a response it repeatedly asks "Hello, are you there?" or "Still with me?" 4. Call quality degradation - audio latency and dropout issues VAPI Configuration: - Telnyx numbers are purchased through Telnyx -portalNumbers are registered in VAPI against Telnyx-generated phone number UUIDsSame VAPI assistant configuration used for both Twilio and TelnyxUsing VAPI's outbound call API to initiate transfers Example one of the affected phone number: +17868408289 (Telnyx VAPI ID - 89d82be1-dc7e-4955-ab9c-c84fd2c68265) Given that the behavior only occurs with Telnyx numbers and not with other providers, we suspect there may be an issue related to media handling, latency, or voice/VAD configuration. API For for sending assistant data and phone number https://api.vapi.ai/call const reqBody = JSON.stringify({ assistant: {} //Json Assistant, phoneNumberId: 89d82be1-dc7e-4955-ab9c-c84fd2c68265 //Telnyx Vapi ID, customer: { number: destination Number // eg +1 12384081234 } }); Its is happening with all telnyx numbers which is registered in vapi. Sharing logs and details of one of the call: Phone Number: +17868408289 Telnyx Vapi ID: 89d82be1-dc7e-4955-ab9c-c84fd2c68265 call id : 019c0dc9-647c-7aa5-8f36-cc3e10983a9a Could you please help us investigate this further? Let us know if you need any additional details, logs, or configuration information from our side. @Zack

I’ve worked on VAPI + Telnyx and have seen similar issues before. Since the same assistant works fine with Twilio, this does point to a Telnyx media/VAD or audio stream handling mismatch in VAPI. Happy to help you debug this we can review Telnyx call media settings, codec/VAD configs, and VAPI phoneNumber setup to isolate the latency and hallucination behavior. I can also help analyze the call logs and suggest concrete fixes. @Riddhi Balar

@Adam Thanks for the help. What would be most helpful for you to review first? Should I send over the configs or set up a time to go through this together?

Send me a message

@User Any update on this?

Hi @Riddhi Balar sorry this slipped through on our end. I'm looping in the team now and we'll get back to you with an update asap. Thanks for your patience!

@User Have you had a chance to find any leads on this issue? It’s currently blocking us, so any update would be greatly appreciated.

looking into this

Hey Riddhi, I'll be looking into this. Can you provide a few new call IDs for the latency issues? We don't have logs for older calls shared above.

Hey Sarthak, Here are some new Call IDs from 02/03/2026 for your reference: 019caee2-ef7e-777a-b6c3-4ca280b7d4f7 019caef7-55b4-799a-9490-cba469807816 019caefc-0d2a-7339-9da6-da606668bbaa I’m happy to schedule a meeting to help resolve this as soon as possible. Please let me know if any additional support is required from our end.