Mod compatibility

I'm also having a issue getting extensions to upload, when I attempt to upload the file with the correct options in the admin section nothing happens.
I'm trying to install a PayPal extension which states it is 4.0.0 compatible but does not seem to work.

Gonna need more details. What do you see when you try to install? Are you installing from the installer/marketplace in the admin or another way?

I don't even see a paypal in the store that's 4.0 compatible which makes me wonder where all the default payments are for things like paypal, etc.