Help creating an inbound call ai agent from retell or 11labs

Questions
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I am creating this workflow for a local roofing company to me where it takes calls from people calling in and books them as well as adding it to a spreadsheet and sending email with all the information from dates to names and contact as well as service type and such. Which is easy. But the issue im having is figuring out how to implement if the caller cant do the proposed time by the ai. Like how does retell or 11labs respond to the n8n workflow in the middle of the call depending on what the caller says. I have tried loops and ai agents and if nodes and I cannot for the love of me figure out how to do that part. If anyone has any workflows of this sort made or any pointers on how to do this it would be absolutely amazing. Above is my most successful workflow but same thing when it gets to the loop and if node and shows undefined and i just cant get retell to respond to if the user accepts it. Thanks

1 Like
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Hi @pblocher Welcome!
I guess in your case letting 11Labs and Retell handle the TOOLs only would be viable as then they will only be calling n8n webhooks like book_call or available_time when they see a potential Yes/No from the client, i guess this approach would be better in this use case.

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HI @pblocher ,

The problem is that you’re trying to handle the back-and-forth conversation logic (like “can you do another time?”) inside n8n, but n8n can’t talk back to the caller mid-call — it’s not a conversation engine, it’s an automation tool. The fix is simple: let Retell handle all the negotiation during the call (propose times, handle rejections, offer alternatives) by putting that logic in your Retell agent’s prompt and instructions. Then, set up a custom function in Retell called something like book_appointment that only fires a webhook to n8n once the caller has fully confirmed a date, time, name, and service type. That way your n8n workflow becomes a straight line — Webhook receives the final confirmed data → adds a row to Google Sheets → sends an email with all the details → done. No loops, no if-nodes, no agent nodes needed. The “undefined” errors you’re seeing happen because you’re expecting Retell to send mid-call responses back into n8n, which it doesn’t do. Keep the conversation in Retell, keep the automation in n8n, and it’ll work cleanly.

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Ok yeah thank you so much. I knew I was overcomplicating myself. I guess the only question I have to that then is how can I get retell or 11labs to understand my calendar and give open dates if its not coming from n8n.

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would using cal.com be sufficient for me and the company to check and book. Then use n8n as the backend to send confirmation emails and log into sheets? Or is there a better solution you have

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Yes that’s a good option.