Querying Elixir API from a UI

Hi. I’m building a rest API using Phoenix and a UI using VueJS. I have a signup endpoint in the API that returns 400 error code when requesting using my UI, but it returns 201 when using querying from postman.

This works:

curl 'http://localhost:4000/v1/users/signup' -H 'Content-Type: application/json'   --data-binary '{"user":{"email":"dummy@example.com","username":"dummy@example.com","password":"password123456"}}' 

And it fails when the UI issues the requests:

But for some reason when I check the browser devtools I see that the content-type is set to application/json for both response headers and request headers. And I don’t know how, my JS logic explicitly sets the header to ‘content-type’: ‘application/json’