A brief example of working with an external API in WordPress

instagram-fetch.php

<?php
// In this brief example we'll scrape an Instagram post and save it as a WordPress post

// Go to a URL and get the contents back
// See https://developer.wordpress.org/reference/functions/wp_remote_get/
$instagram_request = wp_remote_get( 'https://www.instagram.com/p/BSBvNVIF8tI/' );

// If it's succesful, the payload of the request will be in $instagram_request['body']
$instagram_html = $instagram_request['body'];

// Instagram includes JSON data about the post within the HTML of the page.
// With a bit of parsing we can get that JSON data into something we can use in PHP
// Via https://github.com/raiym/instagram-php-scraper/blob/849f464bf53f84a93f86d1ecc6c806cc61c27fdc/src/InstagramScraper/Instagram.php#L32
$arr = explode( 'window._sharedData = ', $instagram_html );
$json = explode( ';</script>', $arr[1] );
$json = $json[0];
$instagram_json = json_decode( $json );

// To see the data in $instagram_json refer to http://www.jsoneditoronline.org/?id=9e77af0c63b3aab427e2cb506e374a1e 
// Instagram has a very verbose structure for its data that we can simplify to work with
$instagram_node = $instagram_json->entry_data->PostPage[0]->graphql->shortcode_media;

// Let's get the URL src of the image
$img_src = $instagram_node->display_url;

// Lets get the description
$description = $instagram_node->edge_media_to_caption->edges[0]->node->text

// And the Instagram permalink
// i.e. https://www.instagram.com/p/BSBvNVIF8tI/
$permalink = 'https://www.instagram.com/p/' . $instagram_node->shortcode . '/';

// Now let's make a WordPress post
$post_content = '<img src="' . $img_src . '">';
$post_content .= '<p>' . $description . '</p>';
$post_content .= '<p>via <a href="' . $permalink . '">' . $permalink . '</a></p>';

$new_post = array(
  'post_content' => $post_content,
  'post_title' => 'My Instagram Post',
  'post_status' => 'publish',
);

// Create a new post with the details we provided
wp_insert_post( $new_post );

// Now every time this code is run it will fetch data from Instagram, parse it, and save a new post