How do my runs get into Pacexis?
Through the Pacexis phone app. Install it on your iPhone or Android phone and sign in with the same account. When it asks, allow it to read your workouts: Apple Health on iPhone, Health Connect on Android.
From then on, any run your watch or running app saves to Apple Health or Health Connect syncs to Pacexis, on the phone and on the web. There is nothing to connect on the web itself.