I think the main thing from your perspective is to keep it simple but yet professional, and have a way to track what vouchers are issued/used versus not.

It probably won't be an issue for me but you also need to think about what if the voucher recipient wants to use it to buy from the site, will they be able to enter their code and get the value off their order? Not sure if your website can do this or not, or if one of the T&Cs will need to be purchase in person or contact via email before purchase or something like that? You probably do want to keep it simple initially to see what the uptake is like before investing on the technology side to support it, if required.

I mean you could just keep a spreadsheet to track vouchers issued and used, not pretty but should work.

You may also want to only allow certain amounts to make it worthwhile on your side e.g. €25 & €50?

Can I take it something will be in place in the coming weeks or?