"This reader is not supported" on Contactless & Chip reader

Questions
1

Environment:

  • Mobile Payments SDK version: 2.4.0 (Android)

  • Android API: 34 (targetSdk), compileSdk 35, minSdk 28

  • Device: RK3566 tablet (GMS certified, Google Play Store + Play Services installed)

  • Reader: Square Reader for Contactless & Chip (2nd generation)

  • Reader firmware: 411092

  • App package: com.golfmark.express (production, not sandbox)

  • Application ID: starts with sq0idp- (production credentials)

  • SHA-256 fingerprint: registered in Square Developer Dashboard

Issue:
After pairing a Square Reader via Bluetooth, the SDK’s built-in Settings UI shows:

Reader unavailable
This reader is not supported. Try again with a supported reader.

The reader IS connected — battery level, firmware version, and serial number are all visible. The Bluetooth pairing succeeds, but the SDK rejects the reader as “not supported.”

What works:

  • The official Square POS app on the same tablet pairs with the same reader and processes payments successfully

  • The reader is a 2nd generation Contactless & Chip reader (S222) which is listed as supported

  • SDK authorization succeeds (authorizationState.isAuthorized = true)

  • SDK environment is PRODUCTION (not sandbox)

  • All permissions granted (Bluetooth, Location, Phone State, Microphone)

What I’ve tried:

  • SDK versions 2.3.0 and 2.4.0 — both show the same error

  • Verified SHA-256 fingerprint matches Square Developer Dashboard registration

  • Confirmed production Application ID (sq0idp-…) and production access token

  • Verified device is not rooted (release-keys, verified boot green)

  • Developer Options is disabled

  • Completely uninstalled and reinstalled the app

  • Forgot and re-paired the reader

Timeline:

  • The same APK + reader combination worked on March 6 and successfully charged

  • After flashing the updated GMS firmware and updating Google Play Services, the reader now shows “not supported.”

  • Even reinstalling the previously-working APK now produces the same error

Questions:

  1. What does “This reader is not supported” specifically mean in the SDK’s built-in Settings UI? Is this a device compatibility check, reader firmware check, or backend validation?

  2. Is there a way to get the exact ReaderUnavailable.reason code behind this message?

  3. Are there known device attestation / Play Integrity requirements that could cause this on a GMS-certified non-Samsung/Pixel device?

  4. Does the reader firmware (411092) need to be updated to work with SDK 2.4.0? If so, how — since the SDK settings screen doesn’t offer an update option?

Any help would be appreciated. The official Square POS app works perfectly on this device, so I believe the hardware is compatible — something in the SDK’s validation is rejecting the reader.

2

:waving_hand: I’m Square Dev AI, here to help answer your question!
Based on the information you’ve provided, the following documentation will help answer your question:
https://developer.squareup.com/docs/reader-sdk/build-on-android

Additional Documentation

https://developer.squareup.com/docs/reader-sdk/what-it-does
https://developer.squareup.com/docs/reader-sdk/cookbook/contactless-reader
Mobile Payments SDK

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