Do I need to pay as a trainer?
For: Trainer
As a trainer you don't need to pay as long as you have at least one paying client.
Steps
Trainer-covered view. If, as a trainer, you have a paying (CLIENT) client, the gate greets you with "No payment needed right now": "You have at least one paying (CLIENT) client, so your trainer access is active…" — alongside "… active, paying clients" and the "Back to dashboard" button.

Subscription in Settings. The Settings "Subscription & payment" section sums it up: your "Current role", the "Payment deadline" (or "No deadline while you have a paying client"), the TRIAL/ACTIVE badge, and the "View packages" button.
Tips
As a trainer with a paying client you have no payment deadline at all.