Hi, I am trying to set up and activate a gift certificate without making a purchase on the web, or assigning a customer, does anyone know how I can or should I do it?

Well you could do it in NetSuite using a sales order

If I do it by sales order I should make a payment to activate it, is there a way to activate it without making a payment?

Well, I don't know the best way to do this operationally. If you're trying to give a customer a gift certificate for free (eg because they won it as a prize) then you will need to account for it somehow, and I don't know the best way to do that from a financial POV

Do you know if I can configure that only one person can use the active gift certificate?

I actually don't know if the gift certificate can be restricted to a single person. But after a person has a gift certificate created for them they will be sent a code they can use to redeem it, so I don't know if technically anyone can use the code or if it's locked to that person

Yes I have read it, but it says what you just told me, the code is sent to the mail, however, whoever receives the code can share it with other people who are not him, that's why I was asking if you had any knowledge of restrictions or something like that.

Yes, I am reasonably sure it can be shared. An alternative would be to generate a SuitePromotions code and limit it to single use and the audience to a single person. However, this is not a gift certificate and only gives a discount. So if the promo gives $100 off and they buy $70 of stuff, they will 'lose' the $30

Yes, exactly, I am looking at how to do it but I see that it is not possible, thank you very much for your help.