为了使我的简单Ionic 3 WebApp GET请求正常工作，我需要在REST-API响应中设置哪些标头？

Question

I'm stuck in creating my first Ionic app.

Scenario:

1. Created a simple REST-API with Golang. It's working fine when i make the GET call in browser and / or Postman. The Output is:

   [
       {
           "id": 1,
           "name": "Leanne Graham"
       },
       {
           "id": 100,
           "name": "I COME FROM YOUR OWN REST-API!!!"
       }
   ]
   

2. I created a simple Ionic 3 (with Angular 5) web app based on some tutorials. I just wanted to diplay my test data in an ionic-list with ngFor. This is working fine with some static (hard-coded) data.

3. I then switched from hard-coded data to a REST-API. The tutorial suggested me to use http://jsonplaceholder.typicode.com/users. This also worked fine; I was able to display the users' data (tried only with id and name) in my ionic-list.
4. I then switched to my own REST-API. I took similar (a little less) JSON content like the one from http://jsonplaceholder.typicode.com/users. See above.

Problem:

My ionic-list stays empty after fetching data from my own REST-API but works with any other public API.

Thoughts:

• Since the content of my REST-API response is nearly the same as the one from http://jsonplaceholder.typicode.com/users i guess there is something wrong in my api-response headers. No tutorial covers the header stuff. This is why I didn't set them. I tried different headers in my response like w.Header().Set("content-type", "application/json") but this doesn't help.
• Are there general headers I always have to set when responding to a GET request from an Ionic app?
• When helpful I naturally will post my app's code here.