Why do I receive the error "The folder already exists" when installing the plugin?

Issues like this usually occur when you install the plugin manually, and you unzip ameliabooking.zip inside the "ameliabooking" folder, so instead of ../wp-content/plugins/ameliabooking/ you have ../wp-content/plugins/ameliabooking/ameliabooking/

Your website can't install the plugin again, since the top "ameliabooking" folder exists, but it also cannot see the plugin because instead of all this:

It sees only this:

So, you would need to extract all the folders you see in the first screenshot up one level.