Subdomain refers to the platform URL.

When the Mobile App asks you for a subdomain when trying to enter or register from your phone, what you need to place is the name of the platform that appears between "https://" and ".gointegro.com".

For example:

For the following platform: https://mycompany.gointegro.com the subdomain is "mycompany".

To know this information, check the link or URL of the platform in a browser or consult it with the HR manager of your company.