API Subscription Plans
One account can subscribe to more than one API. Each API has its own subscription and its own plans.
Open that API and use the Pricing tab. Plans are listed as Monthly or Annually, with the included calls and the Rate Limit on each plan.
Press Subscribe, or Start Free Trial when that API offers a trial. That opens Stripe Checkout for that API only.
A new API key can access every API the account is subscribed to. Keys are managed at https://zylalabs.com/api_keys, where access to specific APIs can be turned on or off.