Here you can check if you have a guest account. When you click Check a new page will open looking like this
If this is the first time you sign in to the Nexi Extranet, you will be asked to consent to Nexi Group to use your name and profile information. That is necessary for security reasons. If your company is using Microsoft Office 365 you should be good to go.
If you cannot log-on to the Nets Merchants Services IntraNets and get messages such as 'your account was not found', then you will have to create a Microsoft account using your company email address. That will have no impact on your current set-up, it is simply a technique used to ensure that we know that you have access to the mailbox.