403 error on POST from react native to EC2 Spring Boot API

Question

I have this spring boot app running on an AWS EC2 instance and when I make a post request from insomnia in my computer, it works, but, when calling it from my react native app, who's running in my mobile device, it gets a network error. Facing this issue, I've got a postman-like app and made the request through to see what does it returns, then got a 403 error, with no body response attached. May it be a missing inbound config on the EC2 instance? Any help would be very welcome.

(The quoted "Postman-like")App request: https://i.stack.imgur.com/HsZqN.png