> For the complete documentation index, see [llms.txt](https://docs.payments.thalescloud.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.payments.thalescloud.io/nfc-wallet-sdk-ios/additional-features/use-correlationid.md).

# Use correlationID

## Overview

Each Tokenization process has an associated `correlationID` that you can share with Thales to help with troubleshooting.

This identifier can be obtained in two ways:

* From a successful eligibility check or from a Tokenization error.
* You can also assign your own custom `correlationID` when calling `checkEligibility()` .

## SDK integration

### Get correlationID from `checkEligibility(...)`

* After successful `checkEligibility(...)`
  * After a successful eligibility check, read `acceptanceData.correlationID`.
  * Store this value if you need to trace the same Tokenization process later.
* After error on `checkEligibility(...)`
  * Read or store `correlationID` as soon as the error is caught.

The following example explains how to get `correlationID` `checkEligibility(...)`

```swift
// Get correlationID during digitizeCard()
let cardDigitizationService = CardDigitizationService()
let authenticationToken = Data() // Issuer backend token for green flow enrollment.
let fcmToken = "FACY6074293608087656831WRF1234" // Example only.

do {
    try await cardDigitizationService.digitizeCard(
        withTNC: termsAndConditions.accept(),
        pushToken: fcmToken, // Firebase Cloud Messaging (FCM) token
        language: "en",
        authenticationToken: authenticationToken
    )
} catch let error as CardDigitizationService.Error {
    let returnedCorrelationID = error.correlationID
} catch let error as CardDigitizationService.DigitizeError {
    let returnedCorrelationID = error.correlationID
} catch {
    // Handle other errors.
}

for await state in await cardDigitizationService.eventStream {
    switch state {
    case let .digitizationApproved(digitalCardID):
        _ = digitalCardID
        return
    case let .errorEncountered(error):
        if let error = error as? CardDigitizationService.Error {
            let returnedCorrelationID = error.correlationID
        } else if let error = error as? CardDigitizationService.DigitizeError {
            let returnedCorrelationID = error.correlationID
        }
        return
        default:
        break
    }
}
```

### Set a custom correlationID

You can set `correlationID` only in `checkEligibility(...)`.

The following `checkEligibility(...)` variants support this parameter.

Use a custom value when you want to trace a Tokenization process across the issuer backend, the digital wallet application, and Thales logs.

You can also use your own identifier format, for example:

```
ORDER-12345-SESSION-67890
```

#### Set a custom correlationID with instrument data

```swift
// checkEligibility() with card data
let encryptedDataComponent = CardDigitizationService.InstrumentDataComponents(
    publicKey: pubKey,
    identifier: pubKeyIdentifier,
    pan: pan,
    expiryDate: expiryDate,
    cvv: cvv
)
let instrumentData = encryptedDataComponent.instrumentData()
let eligibilityData = "<eligibilityData>"
let correlationID = "<correlationID>"

do {
    let cardDigitizationService = try await CardDigitizationService()
    let acceptanceData = try await cardDigitizationService.checkEligibility(
        eligibilityData,
        instrumentData: instrumentData,
        correlationID: correlationID
    )
    let returnedCorrelationID = acceptanceData.correlationID
    let tnc = acceptanceData.termsAndConditions
} catch let error as CardDigitizationService.Error {
    let returnedCorrelationID = error.correlationID
} catch let error as CardDigitizationService.EligibleError {
    let returnedCorrelationID = error.correlationID
} catch {
    // Handle other errors.
}
```

#### Set a custom correlationID with a pushSessionID

```swift
// checkEligibility() with pushSessionID
let eligibilityData = "<eligibilityData>"
let pushSessionID = "<pushSessionIDFromIssuerBackend>"
let correlationID = "<correlationID>"

do {
    let cardDigitizationService = try await CardDigitizationService()
    let acceptanceData = try await cardDigitizationService.checkEligibility(
        eligibilityData,
        pushSessionID: pushSessionID,
        correlationID: correlationID
    )
    let returnedCorrelationID = acceptanceData.correlationID
    let tnc = acceptanceData.termsAndConditions
} catch let error as CardDigitizationService.Error {
    let returnedCorrelationID = error.correlationID
} catch let error as CardDigitizationService.EligibleError {
    let returnedCorrelationID = error.correlationID
} catch {
    // Handle other errors.
}
```


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