I launched my first app but have no idea what the right pricing model is

I recently launched my first app called Postmarks. It's a step-tracking app where your steps move you along real-world routes through Japan, Korea, and Taiwan, and reaching a new city earns you a collectible postage stamp.

The first route (~150k steps) is free for everyone. Premium unlocks 7 more routes plus "After Dark" mode, where you collect night versions of the stamps.

Conversion has been low so far, and the most common feedback I'm getting is that a subscription doesn't fit the product — people are suggesting a one-time payment or selling route packs instead.

I can see the logic on both sides:

• Subscription rewards me for adding new routes/stamps over time, which is the plan
• One-time / packs matches how people actually think about a "collectible" product — you buy the thing, you own it

For those of you who've shipped paid apps: how did you land on your pricing model? Did you start with one and switch? Any frameworks or signals you used to decide?