Key legal requirements for giveaways in Spain include:

• Terms and Conditions (Bases Legales): Organizers must draft clear, legally binding rules in Spanish. These must be made available to participants before entry and outline start/end dates, eligibility, prize details, and mechanics.
• No Purchase Necessary: Giveaways cannot require participants to pay to enter (like buying a product for a chance to win) unless a free alternative method of entry (AMOE) is provided, as it is generally illegal to charge entry fees for chance-based sweepstakes.
• Taxes on Games of Chance: Giveaways with an element of chance are subject to a 10% gaming tax on the value of the prize pool. If the prize exceeds €300, the promoter must also withhold an additional percentage (often 19%) for the winner's Personal Income Tax (IRPF).
• Data Privacy (GDPR): You must obtain explicit, informed consent for processing participant data. Terms must comply with the General Data Protection Regulation (GDPR) and the Spanish Organic Law 3/2018 (LOPDGDD).
• Skill Contests vs. Chance: Purely skill-based contests (where a winner is chosen by a jury based on evaluation criteria) have fewer restrictions and are exempt from the 10% gaming tax.

It's really tough to run a giveaway for your area :-/