Fixing Cal.com API Integration Error: "Invalid API Key" 502 Bad Gateway

Last updated: May 15, 2026

If you're encountering a 502 Bad Gateway error with the message Cal.com Error: CustomThrottlerGuard - Invalid API Key when trying to book appointments through your inbound agents, this is likely due to an incorrect server region configuration.

Common Cause: Incorrect Server Region Setting

The most common cause of this error is having the wrong server region configured for your Cal.com integration. Even if your API key is valid and works for outbound agents, inbound agents may fail if the server region doesn't match your Cal.com account setup.

Solution

Check your inbound assistant's server region setting:

Exact Navigation Path to Cal.com Server Region Setting

Navigate to Tools > Terminbuchung (Appointment Booking) and scroll down to locate the Server Region field. Update the setting to match your Cal.com account region, then save the configuration.

  1. Navigate to Tools > Terminbuchung (Appointment Booking)

  2. Scroll down to locate the Server Region field

  3. Update the setting to match your Cal.com account region

  4. Save the configuration

Additional Troubleshooting

If the server region fix doesn't resolve the issue, also verify:

  • Your API keys are correctly copied without any extra spaces or characters