Count the days between buying and selling: from 365 days the gain becomes exempt. The autonomous rate is 28%; if you opt for aggregation, replace it with your marginal IRS rate. Costs are the buy/sell exchange commissions.
You held the crypto for less than 365 days, so the gain is taxed at the 28% autonomous rate (Art. 72 CIRS) and reported in Anexo G. You can opt for aggregation and use your marginal IRS rate.
Net amount you receive: €7,124.00
Educational estimate, not tax advice. Covers the sale of crypto-assets by residents (Categoria G); it does not cover crypto-to-crypto swaps (untaxed), staking, mining or professional activity.