# 21200: Calls Resource

Log Level: ERROR

## Description

This error points to a problem with a request to the Calls resource. When you create a call, include `to` and `from`, and provide `url`, `twiml`, or `applicationSid` so Twilio can execute the call.

### Possible causes

* The request omitted the required `to` parameter or `from` parameter.
* The request did not include `url`, `twiml`, or `applicationSid` to provide call instructions.
* The `from` value is not a Twilio phone number or a verified outgoing caller ID, or `to` is a phone number while `from` is not.
* The request used an unsupported value for `method`, `fallbackMethod`, or `statusCallbackMethod`. These parameters only accept `GET` or `POST`.
* The request included an invalid `url` or callback URL. The call `url` must be an absolute URL, and `statusCallback` URLs must contain a valid hostname.

### Possible solutions

* Send the call request as `application/x-www-form-urlencoded` and confirm that all required parameters are present.
* Provide a valid `url`, inline `twiml`, or a valid `applicationSid` so Twilio has instructions for the call.
* If you are calling a phone number, format `to` and `from` in `E.164` and use a Twilio number or verified outgoing caller ID for `from`.
* Use only `GET` or `POST` for method parameters, and make sure every webhook URL is publicly reachable by Twilio.
* Review your Voice logs and the Request Inspector in Twilio Console to identify the exact parameter or webhook that failed.

#### Additional resources

* [Call resource API reference](/docs/voice/api/call-resource)
* [Make outbound phone calls](/docs/voice/tutorials/how-to-make-outbound-phone-calls)
* [Troubleshooting Outgoing Twilio Programmable Voice Calls](https://help.twilio.com/articles/360009924213-Troubleshooting-Outgoing-Twilio-Programmable-Voice-Calls)