Square Reader (2nd Gen) Fails to Connect — SECURE_CONNECTION_TO_SQUARE_FAILURE / INTERNAL_ERROR

Questions
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1

Hi,

I’m encountering connection issues when using the Square Reader (2nd generation). During the connection process, the following errors appear:

ReaderUnavailable(reason=SECURE_CONNECTION_TO_SQUARE_FAILURE)  
ReaderUnavailable(reason=INTERNAL_ERROR)

Details:

  • Time (Pacific Time): 2025-07-21 18:27:00
  • Location ID: LSZEF1V47SWV7
  • Application ID: sq0idp-g7k1G7BSi9k3DVNKzmWpkQ
  • SDK Versions:
    • com.squareup.sdk:mobile-payments-sdk:2.3.0
    • com.squareup.sdk:mockreader-ui:2.3.0

I’m launching the built-in settings UI via:

MobilePaymentsSdk.settingsManager().showSettings()

Shortly after this, the reader attempts to connect but fails with one of the above error messages. It then automatically disconnects or is removed.

From what I can observe, the connection flow seems to be:

  1. Bluetooth connected
  2. Connecting to Square (I assume this means your servers)
  3. Fails with SECURE_CONNECTION_TO_SQUARE_FAILURE or INTERNAL_ERROR
  4. Reader is automatically removed

I’m completely stuck at this point. Could someone help me understand what’s going wrong here?

Thanks a lot in advance!

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:

Additional Documentation

Connect a Contactless Reader
Reader SDK
Pair and Manage Card Readers

If this documentation helped you find a solution, please check the box indicating that this reply solves the problem.
Otherwise one of our Developer Advocates will provide additional assistance shortly.

3

Did you receive an email from Square regarding the status of your account? :slight_smile:

4

I don’t remember receiving it. I don’t see any issues in Sign up for Square.

5

Okay, all looks good now. You’ll also need to add the app signature to connect to a reader. :slight_smile:

6

Thank you for your reply. However, I’m now encountering a new issue:
“This device is not supported. Please try another device.”

I tested the same reader on a colleague’s device, and it connected successfully. But on my vending machine’s Android device, I consistently receive this error message, which is quite confusing. Do you have any suggestions or solutions for this?

Here is the log I captured:

ReaderChangedEvent(change=CHANGED_STATE, reader=ReaderInfo(
    id='F8:44:77:49:42:22',
    model=CONTACTLESS_AND_CHIP,
    state=FailedToConnect(reason=[DeniedReason(
        uxHint=NO_SUGGESTED_ACTION,
        localizedTitle='Device Not Supported',
        localizedDescription='This device is not supported. Please try another device.'
    )]),
    status=ReaderUnavailable(reason=READER_NOT_SUPPORTED),
    serialNumber=444LS22207008231,
    name='Square Reader 8231',
    batteryStatus=BatteryStatus(percent=100, isCharging=true),
    firmwareVersion=402100,
    firmwarePercent=null,
    supportedCardEntryMethods=[],
    isForgettable=true,
    isBlinkable=true),
    readerSerialNumber=444LS22207008231
)

The issue occurred at Pacific Time: 2025-07-28 01:51:11.

7

Is the device in developer mode? What is different about the tow devices? :slight_smile: