I won a competition wherein the prize is a complete pass to Cannes Lion. I will still be talking to the person from their side but I want to prepare beforehand.
Is the purpose of this travel considered a business trip or a visitor trip? What supporting documents will I be needing from Cannes Lions?
Cannes Lions doesn’t seem like a tourist destination to me. It looks more like a conference. That makes it business, not tourism.
With regard to applying for your Schengen visa, all you really need from them is your tickets, or at least some confirmation that you have tickets. If they are covering other costs of your travel, then you also should supply some confirmation of the specific costs they will cover (e.g. hotel, food, airfare, etc.).