If it's a posting issue, you're likely experiencing one of a few things. Your internet speeds may be unstable, so the bandwidth isn't there for you to upload your content. The application may be out-of-date, so head over to your OS's app store and make sure it's updated. Lastly, TikTok may prevent you from posting if you've violated the terms and agreements, including music and images. You should probably check your email for any communication from TikTok if this is the issue.