getDigitalGoodsService consistently returns null / unsupported despite correct configuration (TWA, PBL 7.1.1)

**Environment**
- App: PadelScore (com.remlinpl.padelscore), published on Play Console Closed Testing
- Device tested: Samsung Galaxy S21 5G, Chrome 150.0.7874.183 (default browser)
- androidbrowserhelper: 2.7.1 (billing: 1.1.0, PBL 7.1.1)
- targetSdkVersion: 36, compileSdkVersion: 36

**Issue**
`window.getDigitalGoodsService("https://play.google.com/billing")` consistently
returns null (or the calling code treats it as unsupported) in a TWA installed
from a Google Play Closed Testing track. Purchase flow shows our fallback
"purchases only available in Play-installed version" message; restore-purchase
flow silently falls back to cached (false) entitlement.

**What I've verified is correct**
- assetlinks.json served correctly and matches Play App Signing certificate
(verified via Digital Asset Links Tester — "Success")
- Android App Links verified on-device (domain shows under Settings > Apps >
[app] > Open by default > Supported links)
- 3 subscription SKUs + 1 one-time SKU active in Play Console, all "Active"
status
- AndroidManifest.xml includes PaymentActivity + PaymentService with correct
org.chromium.default_payment_method_name = https://play.google.com/billing
- com.android.vending.BILLING permission added (was missing initially, added
in a later build — no change in behavior)
- App runs as genuine TWA (no address bar visible, confirmed on-device)
- App published and active on Closed Testing track, installed via the tester
opt-in link (not sideloaded)
- Full clean reinstall performed: uninstalled app, cleared Play Store cache,
rebooted device, reinstalled fresh from tester link — no change

**Request**
Could someone confirm whether there's a known issue with Digital Goods API
availability for apps that are very recently published (first Closed Testing
release) or with a small number of opted-in testers? Or any other diagnostic
steps beyond what's listed above?

Happy to share the AAB, twa-manifest config, or Play Console screenshots if helpful.

Start with the AndroidManifest.xml entries for PaymentActivity and PaymentService, then reproduce the issue in the Play Closed Testing installation using window.getDigitalGoodsService("https://play.google.com/billing"). Compare the TWA and Play Billing configuration with the observed fallback behavior; done means identifying a confirmed cause or documenting the remaining diagnostic evidence needed.

Written by the indexing model from the issue text.