To whom it may concern, I’be created a tool using Zapier that cross checks Go High Level to see if a contact exists or not (using the contacts phone number). However, at the end of the zap I need to send that information background Vapi so my voice agent knows whether or not the contact exists, but I can’t find the right endpoint to send that information back to. At the moment I’m using this endpoint: https://api.vapi.ai/v1/assistants/aae731b2-3a05-477c-9397-fc300c2d46d2/webhook But I keep getting this error response when trying to POST back to the endpoint. Any help would be greatly appreciated. https://cdn.discordapp.com/attachments/1402591084328255511/1402591084688834561/09737447-b3f6-40e0-91b4-68e59053622f.jpg?ex=6894783d&is=689326bd&hm=68bf3ad6693edc0cdf7287bc605e6bb3d671d6cf2503658f01213e43d3ff7443&

Thank you for sharing the details and error message. To help you further, could you clarify whether you have set up a custom tool or function in your Vapi assistant to receive data from Zapier (such as an API Request Tool or MCP integration), or are you trying to POST directly to a default Vapi endpoint? This will help determine the correct way to send information from Zapier back to your voice agent. Sources: - [Setting Server URLs](https://docs.vapi.ai/server-url/setting-server-urls) - [MCP Integration](https://docs.vapi.ai/tools/mcp) - [API Request Tool](https://docs.vapi.ai/api-reference/tools/create?explorer=true)

Remove webhook from your url and run it again

Use the dynamic callbackUrl provided by vapi in the tool call request, and POST your result including toolCallId and outcome back to that URL in the required JSON format..

I saw that suggestion online as well, but I can’t seem to find the callbackUrl in the tool request

Kindly reach out to me in DM. I'll help you

Vapi tools don’t provide a callbackUrl; instead, you set a Server URL in the tool, and that’s the endpoint your Zapier POST should target to send data into the assistant..