### Answer --- The "check availability" working but "book appointment" failing is a common issue with Cal.com integration. Based on community reports, here are the most likely causes: *1. Missing required fields (most common) * The booking API requires specific fields. The error often indicates the

name

field is missing or not being passed correctly. [(1) ]() Make sure your function description explicitly instructs the agent to collect and include the user's name when calling the book appointment function. 2. usernameList / host configuration Add the correct

usernameList

with the proper host(s) to the booking request. [(2) ]() 3. Time format and timezone issues Double-check that the time format and timezone match what Cal.com expects. Troubleshooting steps: 1. Check your Cal.com event type settings—ensure all required booking questions (name, email, phone) are properly configured [(3) ]() 2. Update your function description to explicitly require collecting the user's name before booking [(1) ]() 3. Test with a simple single-host event first [(2) ]() 4. Verify your API key and Event Type ID are correct in the book appointment function [(4) ]() One user reported: "Turns out there was a setting mix-up with cal.com - all working fine now" after reviewing their Cal.com configuration. [(1) ]() Can you share the specific error message you're seeing in the call logs? That would help narrow down the exact issue.

​ To learn more, see the sources I considered: [[1] Cal.com booking issue](https://discord.com/channels/1186424376300679209/1453799922821496955) [[2] Cal.com Appointments](https://discord.com/channels/1186424376300679209/1358842036635173104) [[3] Retell AI - How to use Cal.com Custom Field]() [[4] Book Calendar](https://docs.retellai.com/build/book-calendar) ​

Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.

Appreciate the feedback! Feel free to ask me again with additional guidance or context.