our project uses blockcypher to create eth wallet which can transfer eth now.Blockcypher supports ETH main network and its own testnet. Is there any way to connect the blockcypher node to a custom testnet such as https://sokol.poa.network?
There is no way to connect POA testnet to the blockcypher. BlockCypher runs the Main and Test Bitcoin, Ethereum, Litecoin and Dogecoin block chains.
POA has its own Ethereum-based network.