I have imported my seed from CakeWallet to MyMonero on iPhone, but MyMonero wallet balance shows 0 XMR.
What is the problem?
Don't import it, just create an entirely new wallet on MyMonero and just send all your coins from CakeWallet to MyMonero. This gives you the following benefit:
Don't import just send the entire thing over.
But if you want to keep your old transaction history for whatever reason, you'll have to pay that import fee.