How to coordinate two /api endpoints in next.js?

Question

React

There is an existing backend written in java. I was going to write a client using next.js.

Now the backend hangs behind the loadbalancer on the path example.com/api. next.js has an API Routing feature, page/api/* , which I also think to use. To receive data from other apis requiring a secret key.

How to mix them correctly? I mean java backend and /api next.js? Hanging a backend for example on /back, but somehow ugly. Hang next.js app on /blog?