I have a problem with the last code for this module, i have done the first 2 successfully but the last code is not running, i have trouble shot and everything but its not working even after 2days of trying, what should I do to complete this module?

Hi, check if the channel is set to public. 

Error: We can't find the say hello (local) app direct messages in this workspace. Make sure the app is only installed in this workspace and try again.