Impossible to activate goods return functionality

[web_gatt]

Hi to everyone,

my prestashop version in 1.6.1.20.

Inside my shop online I can't activate goods return functionality. I have followed the steps to activate the function: inside the backend I have enabled returns and set a time limit of validity of 20 days. Despite this on the frontend, inside the account area, in the section "my returned goods" I see the message "You do not have permission to return goods.". Also inside the "Order History and Details" area I can't see the checkbox which allows to select a product to request the restitution.

Can someone suggest the reason of this problem?

Thanks.