I have mentioned above which thread is relevant with the deeper insight (not only a guide and complaints it doesn't work for me)
Shortly about the terminology
A13+ means Android 13 or higher
<A13 means strictly lower than Android 13, thus Android 12 or lower
It is related to the SDK level
A13 = SDK level 33, thus A13+ means SDK level 33 or higher
A12 = SDK level 32, thus <A13 means SDK level 32 or lower
It is related to the deviceAttributes, sdkVersion in the PI Verdict Json - see the attached screenshots
One is showing Device Integrity with sdkVersion 32, so that was <A13 PI test relevant for Wallet (you must pass that to be able to use Wallet; but Wallet may need up to 72 hours to start working again if it was previously lost)
The other is showing Strong Integrity with sdkVersion 35, so that was Strong for A13- and although nice to have, that Strong is really not relevant for Wallet
To trigger <A13 test you have to TEMPORARILY set
"spoofVendingSdk"' :"1"
in the custom.pif.json - assuming you're using PI Fork module.
And then run killpi sh script
If you use PI Fix Inject, take your time and find how is that exactly named in the WebUI menu (there is the option for, press and follow if asked something)
Then test with PI API Checker (NOT from PlayStore Dev Options !!!!!)
and after the test press <> button top-right, scroll down and read what it says for this sdkVersion
After the test REVERT BACK to A13+:
"spoofVendingSdk"' :"0"
And again run killpi.sh script
Or, In the PI Fix Inject, disable that option in WebUI menu that I mentioned above
That is just top of the iceberg. There are other considerations you must be aware when testing <A13. I will not repeat them here, you can find it in the relevant thread, please particularly carefully read eg this post:
https://xdaforums.com/t/module-play-integrity-fix.4607985/post-90312341
Eg, it is described in details in that post about the pop-up errors you may experience when trying to test <A13, and how to address them
Also, it is emphasized there about the problems with PlayStore you will have if you don't revert (quickly) to the A13+ set-up after the <A13 test
Btw, this notation and terminology A13+ and <A13 might be confusing, maybe sdk33+ and sdk32- or so could be easier to understand, but that's how it is, it was introduced by others.
It actually reflects the changes Google made on May 20 this year - A13+means the new PI Attesting for A13+ (Android 13 and higher), while <A13 means simulating the PI attesting as for the Android 12 and older devices (legacy PI attesting)
And Wallet apparently (still) internally uses that Legacy PI attesting (both for legacy and A13+ devices) to check if the phone meets required security requirements
That's the reason why to test that legacy <A13 PI on our new A13+ phones, to make sure that Wallet will work