The plugin uses 2 services to optimize the use of the characters in the message when it includes a link. You can either choose to use Bitly or TinyUrl.
By enabling Bitly, any address included in the message body will be turned into a shorter link that will still lead to the same address.
First, how to register a Bitly account?
1- register a free account on https://bitly.com/ website
2- once logged in click in the top-right button
3- click on “Profile Settings”
4- click on “Generic Access token”
5- insert your password and click on generate token.
6- in the popup that will appear click on “Copy” button and insert it in the relative plugin field
