Affiliate Marketing in EU - HOW?

Hey IH, I was wondering, if you want to create an affiliate marketing program for a product based in Europe - how much redtape does this involve?

Like - do affiliates need to sign an agreement? Do they need to give you an invoice for the payout so you can do your taxes? How in general this is done?

I couldn't find any meaningful information in regards to that. There're lots of tools for tracking affiliate links, tools that help you with payouts, but none of them mention taxes or legal.

I've found that LemonSqueezy is not only a Merchant-of-Record for payments, but also they can act as a middleman for affiliates. So I'm wondering if this is a big value-added or not necessarily...