Building an integration from an ATS to Bizimply can be done using the Bizimply HR APIs as documented here.

Firstly, request the company_id from Bizimply or the customer for the account in question.

You'll need to get the list of locations and their IDs. To do that, call the company locations endpoint.

Then, using one of those location IDs, when an employee is "hired" in your ATS, you would make a call to create an employee in the Bizimply system.