RestSheet is a free (for now) service that let's you manipulate Excel files via REST APIs. It is free because we don't keep a copy of any file and it is built using free hosting from webflow.io and gigalixirapp.com.
It is a tool designed for developers where you can upload, write and read an excel files on the fly.
There is only one API endpoint which is https://excel-to-api.gigalixirapp.com/api/changeset
and it accepts the format form-data
(as you can see in the example below) and the Bearer token as a form of authentication.
If you get a 500 double-check the cell numbers and sheet names.