2FA (Two-Factor Authentication) is required to trade with other players. Both trading players must have 2FA enabled on their Epic Games accounts.
For more info check out: Two-factor Authentication And How To Enable It
2FA can only be enabled on full Epic Games accounts.
For more info, check out: How Do I Upgrade a Platform Account to a Full Epic Games Account?
If you have already enabled 2FA, be sure to verify your Epic Games email address. For more info on verifying your email address check out: How Do I Verify My Email Address?