> For the complete documentation index, see [llms.txt](https://developers.esms.vn/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://developers.esms.vn/en/readme/mechanism.md).

# Mechanism

Messages can be sent over the HTTP protocol using both POST and GET methods.

Every request will be authenticated using a pair of keys known as APIKEY and SECRETKEY, which will be provided after you register an account at eSMS.vn.