Please place numerous Debug.Log statements in your purchasing code to follow the flow and provide the device logs via XCode How To - Capturing Device Logs on iOS Also, I might recommend adding the following code and add similar Debug.Log statements. These callbacks generally do not provide additional transaction information, but simply and immediately let you know that you should expect a ProcessPurchase some time in the future. It’s not determined if the stores would call these callbacks in the SCA flow.
The iOS Ask to Buy deferred listener is described here:
For Android, the code would look similar to:
m_GoogleExtensions = extensions.GetExtension<IGooglePlayStoreExtensions>();
m_GoogleExtensions?.SetDeferredPurchaseListener(OnPurchaseDeferred);