I believe you have followed EOSBlock/EOS-Tutorials documentation. If so then you have to add the chain ID into the payload of sign_transaction.
[
{
"ref_block_num": 246190,
"ref_block_prefix": 1753012779,
"expiration": "2018-05-24T15:30:32.000",
"actions": [
{
"account": "eosio.token",
"name": "transfer",
"authorization": [
{
"actor": "eosio",
"permission": "active"
}
],
"data": "0000000000ea305500000000487a2b9d102700000000000004454f53000000001163726561746564206279206e6f70726f6d"
}
],
"signatures": []
},
[
"EOS6gXwNz2SKUNAZcyjzVvg6KdNgA1bSuVzCr8c5yWkGij52JKx8V"
],
""
]
This is probably the data you have passed. There is a blank filed "" just below the signatures field. Add chain ID into that field and try again.
If it is not working or it was not the problem, share your error log. So that we can discuss deeply