Madoko (Salvation)

Make sure you have Gems or Items and Units that can be traded for trade fees, for trade fees you can see here
Rare skins - 50 Gems
Epic skins - 100 Gems
Legendary skins - 200 Gems
Mythical skins - 2000 Gems
Mythical relics - 2000 Gems
Epic units - 200 Gems
Legendary units - 400 Gems
Mythical & Secret units before evo - 4000 Gems
Mythical & Secret units after evo - 6000 Gems