Help using acf/save_post hook to connect to Untappd API and update_field [closed]

It’s because your require_once 'Pintlabs/Service/Untappd.php'; is relative to “current” file and should be absolute path. I don’t know where are you using this hook but depending on location it should look something like this:

1. ABSPATH is your wordpress root dir and ‘custom-path’ should be a path to Pintlabs dir
   require_once ABSPATH.'custom-path/'.'Pintlabs/Service/Untappd.php';

2. get_template_directory() if you use it inside your theme (functions.php etc.). Notice the additional "https://wordpress.stackexchange.com/" after get_template_directory()
require_once get_template_directory().'/custom-path/'.'Pintlabs/Service/Untappd.php';

3. plugin_dir_path( __FILE__ ) when inside a plugin. You must use this function in your plugins main file like /my-plugin/my-plugin.php or otherwise you get plugins subdirectory. It’s best to store it using define() in plugins main file.

   in my-plugin/my-plugin.php
define("myplugin_dir",plugin_dir_path( __FILE__ ));

   somewhere else
   require_once myplugin_dir.'/Pintlabs/Service/Untappd.php';