fix message sending logic.

api/eth_transactions.go

@@ -150,12 +150,17 @@ func (tx *EthTxArgs) ToSignedMessage() (*types.SignedMessage, error) {
 			return nil, err
 		}
 		to = addr
+
+		if len(tx.Input) > 0 {
 			var buf bytes.Buffer
 			if err := cbg.WriteByteArray(&buf, tx.Input); err != nil {
 				return nil, fmt.Errorf("failed to encode tx input into a cbor byte-string")
 			}
 			params = buf.Bytes()
 			method = builtintypes.MethodsEVM.InvokeContract
+		} else {
+			method = builtintypes.MethodSend
+		}
 	}
 
 	msg := &types.Message{