Showing unsupportive format

Please use the free MediaInfo and post a screenshot of the properties of your media in tree view:
https://mediaarea.net/en/MediaInfo

Many users are having issues with VFR. If the file is variable frame rate, use Handbrake to convert to constant frame rate before importing into Premiere Pro:
https://handbrake.fr/downloads.php
Here is a tutorial:
https://www.youtube.com/watch?time_continue=34&v=xlvxgVREX-Y

Shutter Encoder may also be used to convert to Constant Frame Rate:
https://www.shutterencoder.com/en/

Please be more specific with your issue. Where did this mp4 come from, did you convert it yourself, are you able to open it in a media player or is it corrupted? If you did make it yourself, try exporting it again or converting it to another format like ProRes.