I've build an app using a tutorial here on the AWS website to build an app and integrate AWS Amplify for authentication etc. I have followed all the steps to the letter, yet when I launch the app I get the following run time error: Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value It is marked against this line: let hostURL = "https://\(webDomain!)" webDomain is a variable assigned a value here as follows: let webDomain = infoDictionary?["WebDomain"] as? String This is in the file AWSMobileClient.swift. Does anyone have any idea where I might look to fix this? I've googled everything phrase I can think of to no avail! Thanks for reading, Mark