fetch("https://api.geoapify.com/v1/boundaries/consists-of?id=51ecbccfa440182740598d7dd2e49a134840f00101f901dcf3000000000000&geometry=geometry_1000&apiKey=YOUR_API_KEY")
.then(resp => resp.json())
.then((boundariesGeoJSON) => {
	console.log(boundariesGeoJSON);
});

Angular

import { Component, OnInit } from '@angular/core';
import { HttpClient } from '@angular/common/http';

@Component({ selector: "app", templateUrl: "app.component.html" })
export class AppComponent implements OnInit {
  
  constructor(private http: HttpClient) { }

  ngOnInit() {      
    this.http.get("https://api.geoapify.com/v1/boundaries/consists-of?id=51ecbccfa440182740598d7dd2e49a134840f00101f901dcf3000000000000&geometry=geometry_1000&apiKey=YOUR_API_KEY")
    .subscribe(boundariesGeoJSON => {
     	console.log(boundariesGeoJSON);
     })
  }
};

Node.js-fetch

const fetch = require('node-fetch'); // run "npm install node-fetch" to install

fetch('https://api.geoapify.com/v1/boundaries/consists-of?id=51ecbccfa440182740598d7dd2e49a134840f00101f901dcf3000000000000&geometry=geometry_1000&apiKey=YOUR_API_KEY')
.then(resp => resp.json())
.then((boundariesGeoJSON) => {
	console.log(boundariesGeoJSON);
});

cURL

curl -XGET "https://api.geoapify.com/v1/boundaries/consists-of?id=51ecbccfa440182740598d7dd2e49a134840f00101f901dcf3000000000000&geometry=geometry_1000&apiKey=YOUR_API_KEY"