didReceive-updated.swift

 override func didReceive(_ request: UNNotificationRequest, withContentHandler contentHandler: @escaping (UNNotificationContent) -> Void) {
        self.contentHandler = contentHandler
        bestAttemptContent = (request.content.mutableCopy() as? UNMutableNotificationContent)

        guard let bestAttemptContent = bestAttemptContent, // 1. Make sure bestAttemptContent is not nil
            let apsData = bestAttemptContent.userInfo["aps"] as? [String: Any], // 2. Dig in the payload to get the
            let attachmentURLAsString = apsData["attachment-url"] as? String, // 3. The attachment-url
            let attachmentURL = URL(string: attachmentURLAsString) else { // 4. And parse it to URL
                return
        }
        // 5. Download the image and pass it to attachments if not nil
        downloadImageFrom(url: attachmentURL) { (attachment) in
            if attachment != nil {
                bestAttemptContent.attachments = [attachment!]
                contentHandler(bestAttemptContent)
            }
        }
    }