Invalid call. Nonexistent function 'isReady' in base 'Nil'.

[vinciarts]

Hi, I followed the doc step by step and also fixed the product_details_query_completed name.
On Mac, When I call payment.isReady() I received this error.
On Android, the payment is not working.

Godot 4.0.1
godot-google-play-billing 2.0.0-rc.1

[Chrompower]

I have the same issue, using Godot 3.5

[NianoTT]

The error means the Play Billing singleton is not available. You should check for it before using it, so it doesn't error out on platforms other then Android:
if Engine.has_singleton("GodotGooglePlayBilling"):

It's only available when running on Android and have a custom export with the Plugin enabled. It will not work in the desktop editor. (Android Build Template also needs to be installed from Project menu)

[kyadalu1]

Try this