Not sure what a REST API is? Or what you can do with them in Power BI? Find out how you can easily take advantage of them without having to write a bunch of code. Use PowerShell instead!
REST API Reference Documentation
https://docs.microsoft.com/rest/api/power-bi/
Power BI PowerShell Reference Documentation
https://docs.microsoft.com/powershell/power-bi/overview
Use Microsoft Flow, and other options, to refresh your Power BI dataset
https://www.youtube.com/watch?v=ClmZ-8p6x9g
Refresh Dataset In Group API
https://docs.microsoft.com/en-us/rest/api/power-bi/datasets/refresh-dataset-in-group
Refresh History in Group API
https://docs.microsoft.com/en-us/rest/api/power-bi/datasets/get-refresh-history-in-group
Get Pages in Group
https://docs.microsoft.com/en-us/rest/api/power-bi/reports/get-pages-in-group