Raising Dragons

[RexHome]

How do I raise my dragons pass level 10?...when I get to level 10 it tells me I?ve reached my max level but in some requests it is asking me to raise my dragons to 11 or to 15 but yet it won?t let me do so...what do I need to do?...thanks

[CranberryMil]

Buy the Noble Crystal in the market to level up to level 15