You need the Steam Guard Mobile Authenticator active on your Steam account, and you must wait 15 days after enabling it before you can trade.
Why do I need the Steam Guard Mobile Authenticator?
Steam requires it for trading. Without it, you cannot trade, sell or buy skins on SkinSwap. You can enable it in the Steam mobile app.
What is Steam trade protection?
Steam applies a 7-day trade protection period to trades. This affects SkinSwap in three ways:
CS2 sales: your payout is sent once the 7-day trade protection period ends. Rust sales are paid instantly.
Reversing a CS2 sale: if you reverse a CS2 sell trade on Steam during the 7-day period, your payout is cancelled and your SkinSwap account is banned. Contact us first if something is wrong.
Trade-locked items: items you buy that are still trade-locked go to your Backpack. You can withdraw them once the lock ends.
When trade protection ends, the trade completes automatically. Reversing any trade with SkinSwap leads to a ban; see Trade reversals, chargebacks and bans.
Can I trade after changing my Steam name or password?
Not straight away. Steam blocks trading for 2 hours after either change.
Related articles: When will I get paid?, The Backpack, Trade reversals, chargebacks and bans