Get the App Store receipt from the Bundle for an app.

AppStoreReceipt.swift

// Derived from code sample in this article: 
// https://developer.apple.com/documentation/storekit/in-app_purchase/validating_receipts_with_the_app_store

// Get the receipt if it's available
if let appStoreReceiptURL = Bundle.main.appStoreReceiptURL,
    FileManager.default.fileExists(atPath: appStoreReceiptURL.path) {

    do {
        let receiptData = try Data(contentsOf: appStoreReceiptURL, options: .alwaysMapped)

        let receiptString = receiptData.base64EncodedString(options: [])
        print(receiptString)

    }
    catch { print("Couldn't read receipt data with error: " + error.localizedDescription) }
}