Sorry for answering in English because we're not offering technical support with other languages. When I checked your account, it seems your data plan is 'Subscription'.  For this plan, you should equip at least one paid item to use all mudfish nodes.

I mean I have bablance, but I cant equip(buy) any item :(

Could you please try it again?  I think you don't have enough balance to equip one paid item. :-)