The Friendship Bonus is automatically credited to your player account once the campaign requirements are met.
You can follow the status of the bonus and the respective playthrough of the friend(s) by accessing the "Account Menu" (icon in the upper right corner) » "Account » Invite your friends". ” (icon in the upper right corner) » “Invite your friends”.
After fulfilling all the conditions and reaching 100%, the Friendship Bonus is automatically credited to your player account.