You can learn information about Bitrix24 REST API from the Bitrix24 REST API Training Course.
What is Bitrix24 API open for?
Is there documentation on Bitrix24 API?
All documentation on REST API for developers can be found on the training page.
Is REST API available on a free plan?
From January 1, 2021, Bitrix24.Market apps, REST API and webhooks (local integrations in the Developers section) is available only on commercial plans.
Read more in the article Important changes in REST API, Market, Telephony and Search.
How to get a consultation on API?
If you have a problem with a particular method or a technical question, you can go to Bitrix24Care Helpdesk or write to Bitrix24 Support for consultation - only for commercial plans.
You can read how to write to Bitrix24 Support in the articles: