How to fix APT KEYEXPIRED 1515625755

This error is caused by an expired GPG key that is used in the MongoDB repository.

This key has already been renewed, but you need to tell GPG to update it. Run:

sudo apt-key adv --keyserver hkp:// --recv 0C49F3730359A14518585931BC711F9BA15703C6

For more details, see this GitHub post.