Plugin could not be deleted due to an error: Could not fully remove the plugin(s) my-plugin/my-plugin.php

I also had the same problem. It was due to the permission issue in wordpress directory. Navigate to the Directory where you have installed WordPress and….
run the following in your terminal:

sudo chown www-data:www-data * -R 
sudo usermod -a -G www-data username

Replace username with the username you are using like root.