Twilio

1. REST API basics

   Resources, requests and response format.

2. Authentication and API keys

   Account SID, auth tokens, API keys.

3. Programmable messaging

   Sending SMS and MMS and using messaging services and senders.

4. Messaging compliance

   A2P 10DLC brand and campaign registration for US messaging.

5. Webhooks

   How Twilio sends HTTP requests to your webhooks and expects responses.

6. Webhook security

   Validating the X-Twilio-Signature header on incoming requests.

7. Voice

   Making and receiving phone calls with the Voice API.

8. TwiML

   TwiML verbs that tell Twilio how to handle a call or message.

9. Verify

   Verifying users with one-time passcodes over SMS, voice and email.

10. Conversations

    Omnichannel conversations, participants and messages.

11. Video

    Video rooms, participants and tracks.

12. Studio

    Studio flows built visually to handle messages and calls.

13. Error and warning dictionary

    The error and warning dictionary of numeric codes.

14. Test credentials

    Test credentials and magic numbers for testing without charges.

15. Subaccounts and usage

    Subaccounts for isolating usage and credentials.

Each section links to the official page. Titles and summaries by Extra Credit; the docs belong to their authors.