There are three potential "missing" messages that you may be seeing:
Missing plugins: Some templates use third-party effects & plugins that don't come standard with your editing program. You can check for any third party plugin requirements on a template’s Details page.
Missing files: This message usually appears if the .zip file hasn't extracted properly. For Windows users: try right-clicking the zip file and choosing "Extract All", and then try opening the file again.
If that option is not available, try using a different extraction program to unarchive the file. We also have a video tutorial on how to relink missing files as well.
Missing fonts: Occasionally, artists use specialized fonts in templates that may not come standard with your editing program. (A download link is usually included with the project.) If you don't install the font, your editing program will typically simply change the font to one already installed on your computer.
In all cases, simply press "OK" and the project should continue opening successfully.
Tutorial Video: How to Re-link Missing Files in Adobe After Effects