The first thing you should check if you can’t send a TikTok DM is to make sure you have a network connection. If you are connected, you should then update your TikTok app to help resolve potential issues. Also, you may need to make sure you have verified your phone number.  Other things that can affect whether you can DM on TikTok is if the feature is disabled on the TikTok app. If the friend you want to DM cannot be found or messaged, they may have their DMs turned off.  Also, if you are still experiencing issues with sending messages on TikTok, go to a site like Downdetector to find out if the TikTok system is down.