Create and broadcast of mulisig-to-multisig transaction via API

I’m trying to create a mulisig-to-multisig transaction using JS and Counterblockd JSON-RPC API.

I have 2 multisig addresses: MS1 = 3_ADDR1_ADDR2_ADDR3_3 and MS2 = 3_ADDR4_ADDR5_ADDR6_3.
Addresses ADDR1 - ADDR6 have private keys PK1 - PK6 and public keys PUB1 - PUB6 respectively.

I want to send 1 coin of my ASSET asset from MS1 to MS2.

First, I created an unsigned transaction using “create_send” Counterpartyd API method.
  method: ‘create_send’,
  params: {
    asset: ASSET,
    source: MS1,
    destination: MS2,
    quantity: 10000000,
    allow_unconfirmed_inputs: true,
    encoding: ‘multisig’,
    pubkey: [ PUB1, PUB2, PUB3, PUB4, PUB5, PUB6 ]

I got a hex of unsigned transaction - UTXhex.

Then I sign this transaction using Bitcoin-JS lib and corresponding private keys.

var tx = Bitcoin.Transaction.fromHex(UTXhex);
tx.sign(0, PK1);  // Sign by ADDR1 of 3_ADDR1_ADDR2_ADDR3_3 address
tx.sign(0, PK2);  // Sign by ADDR2 of 3_ADDR1_ADDR2_ADDR3_3 address
tx.sign(0, PK3);  // Sign by ADDR3 of 3_ADDR1_ADDR2_ADDR3_3 address

var signedTx = tx.toHex();

Now I have a signed transaction hex.
Trying to broadcast it:
   method: ‘broadcast_tx’,
   params: {
      signed_tx_hex: signedTx 

Result: 'Invalid request/response’

Looking deeper I found that Bitcoind throws an exception with code -25 and without any error message.

RPC_VERIFY_ERROR = -25, //! General error during transaction or block submission

So, I have no Idea now what am I doing wrong.
Any help is appreciated!