Start with this quick-start guide:
- http://www.consolibyte.com/docs/index.php/PHP_DevKit_for_QuickBooks_-_Quick-Start
Using this code from GitHub:
- https://github.com/consolibyte/quickbooks-php
Specially, you should be using the files in the docs/web_connector/ folder:
- https://github.com/consolibyte/quickbooks-php/tree/master/docs/web_connector
The file that you mention:
- /dev/dev_ids_customers.php
Is not related to QuickBooks desktop at all, and will not work. That file is for QuickBooks Online, which you are not using. Do not use this file. Use the files in the docs/web_connector/ folder that I have linked to above.
QuickBooks desktop files do not have realm IDs or tokens. You do not need them.