A subdomain is the web version of your mobile app. We call it a PWA or progressive web app. This gives you a web address and your users can access your content via the web either through mobile phone, tablet or desktop. We recommend you have the same name for both your subdomain and web app.
To add your subdomain, go to PassionApps - Basics and enter your subdomain in the app URL field:
Note: The subdomain should have no spaces and only include: lowercase letters, numbers, and dash symbols. No other special characters are permitted.
You can watch the demo on creating your subdomain here: https://passionfighters.passion.io/learn/products/9365/lessons/91310