REST API to call receivables invoice approval workflow

Summary:

Hi All,

We are planning to create VBCS / Apex application which will work as follows-

1) We will pull AR invoices into ATP database

2) User will update the invoice details (like qty , rate) and click submit button

3) Application will trigger OIC integration and update the AR invoice in SaaS (using FBDI / REST API) file

4) AR invoice approval workflow will trigger and follow actual approval hierarchy.

We are good with steps (1 to 3). Can you please suggest how can we trigger AR Invoice approval workflow using REST API? or As soon as we update invoice using FBDI / REST API approval workflow will trigger automatically? Kindly provide some guidance.