How to handle API response in WordPress

I have rest API integrated in site, so when we submit form API responds with code like 201, 401, etc.

201 means success,
401 means error with fields etc.

Thus user get redirected to other page and this response is shown to them. I want to hide this and place simple message at the end of form as success or failed, same as it shown for contact form 7.

Just want to know how to do it?

Thanks