Things can go wrong. But we're going to catalog all the fixes we've encountered here!
ZXP/UXP Installer requires write access to Premiere's CEP directory in order to install your Quickture extension. There are actually a couple of different CEP directories in your Premiere file structure, but the one we are interested in is here:
/Users/your_user_name/Library/Application Support/Adobe/CEP/extensions On a Mac, you can option+click or right click on the extensions folder, then select Get Info to access the permissions. At the bottom of the info window you'll see the permissions for you, staff, and everyone. In order for ZXP/UXP Installer to save the Quickture files in this directory, it needs Read & Write permissions.
So set everyone to "Read & Write". You can change it back after the install is complete!
