How do I find my payment confirmation with the transaction number on my device?

If you didn't get an email with the payment receipt and transaction number, you can check it as follows:

On iPhones or iPads:

Open the Settings app.
Tap your name, then tap Media & Purchases.
Tap View Account. You might be asked to sign in.
Tap Purchase History.

On Android devices:

Go to play.google.com.
At the top right, select your profile icon.
Select Payments & Subscriptions and then Budget & Order History.