Your answer lies in a single concept, and that is Test Automation Pyramid. Below link explains that in detail.
In short, a normal enterprise application consists of multiple layers like UI, API, DB etc. You also need to know what each layer is responsible for. When people talk about test automation, most of them assume that to UI automation. But there is another layer like API(REST) which is providing data to the UI and UI layer only paints that data. So it is really crucial to verify the API layer.
Now I believe what you need is API automation. If your APIs are correct then most of the business logic is already tested and you just need to verify only a sub-part of UI. There are a lot of API testing tools and libraries like soap-UI, RestAssured, python’s Request library etc.
Hope your query is answered.