I have faced the same issue. What you are missing here is the chain ID of the network.

Mainnet: aca376f206b8fc25a6ed44dbdc66547c36c6c33e3a119ffbeaef943642f0e906

Jungle Testnet: e70aaab8997e1dfce58fbfac80cbbb8fecec7b99cf982a9444273cbc64c41473

It has to be added in the " " field just after the key.

Your request for Jungle Testnet should be:

[{
        "expiration": "2018-10-26T15:30:32.000",
        "ref_block_num": 21149807,
        "ref_block_prefix": 3590041248,
        "context_free_actions": [],
        "actions": [{
            "account": "eosio.token",
            "name": "transfer",
            "authorization": [{
                "actor": "testertimohe",
                "permission": "active"
            }],
            "data": "0000000000ea305500000000487a2b9d102700000000000004454f53000000001163726561746564206279206e6f70726f6d"
        }],
        "signatures": []
    },
    ["EOS6gXwNz2SKUNAZcyjzVvg6KdNgA1bSuVzCr8c5yWkGij52JKx8V"], "e70aaab8997e1dfce58fbfac80cbbb8fecec7b99cf982a9444273cbc64c41473"
]
r = requests.post(
    f'http://localhost:8888/v1/wallet/sign_transaction', json=data)
response = json.loads(r.text)

Also make sure that keosd is running at the port 8888.

Good luck..!

What you are missing here is the chain ID of the network.

Mainnet: aca376f206b8fc25a6ed44dbdc66547c36c6c33e3a119ffbeaef943642f0e906

Jungle Testnet: e70aaab8997e1dfce58fbfac80cbbb8fecec7b99cf982a9444273cbc64c41473

It has to be added in the " " field just after the key.

Your request for Jungle Testnet should be:

[{
        "expiration": "2018-10-26T15:30:32.000",
        "ref_block_num": 21149807,
        "ref_block_prefix": 3590041248,
        "context_free_actions": [],
        "actions": [{
            "account": "eosio.token",
            "name": "transfer",
            "authorization": [{
                "actor": "testertimohe",
                "permission": "active"
            }],
            "data": "0000000000ea305500000000487a2b9d102700000000000004454f53000000001163726561746564206279206e6f70726f6d"
        }],
        "signatures": []
    },
    ["EOS6gXwNz2SKUNAZcyjzVvg6KdNgA1bSuVzCr8c5yWkGij52JKx8V"], "e70aaab8997e1dfce58fbfac80cbbb8fecec7b99cf982a9444273cbc64c41473"
]
r = requests.post(
    f'http://localhost:8888/v1/wallet/sign_transaction', json=data)
response = json.loads(r.text)

Also, make sure that keosd is running at the port 8888. And the private key is imported into the wallet and wallet is unlocked.

Good luck..!