You want to verify that the payment will go through properly and want to receive a test payment.
Apps that allow collecting payment are FormBuilder, Payment button, eCommerce, etc.
To make a test purchase kindly change the price to the lowest amount > re-publish the app, then submit a test payment. Once you verify you received the charge, please check your PayPal or Stripe account and check-in POWR Response/Sales Dashboard to see if the payment has been submitted.
Finally, you can set the price back to normal. Please make sure to re-publish the app with the correct price.