My mobile app will not let me log into my trailhead playground. I can log into salesforce & trailheads, but not my p-ground. Any suggestions? I tried various url's. I even used the one i connect with on my computer, success on the computer, not mobile.

My mobile app will not let me log into my trailhead playground. I can log into salesforce & trailheads, but not my p-ground. Any suggestions? I tried various url's. I even used the one i connect with on my computer, success on the computer, not mobile.