How to permanently delete?

I keep getting this persistent message “PayPal Express Checkout could not be installed (Could not copy file.). Please install it manually by clicking here.” on every page in WP-Admin. I’m finding it really bothersome, it keeps coming back after clicking ‘dismiss’. I never installed it. Don’t know why its there?

I decided to install it and then deactivating it before proceeding to delete it as a solution but it says “Plugin cannot be deleted while being used on main site”. I disabled this plugin on Woocommerce settings but it’s still resisting deactivation and deletion.

I decided to delete it via FTP but even after deleting it, my site is incredibly slow. It was really fast before – and my internet connection is fast. It has to be this plugin. It’s definitely not the host, as my host is WP Engine.

Please can you fix this?