Cannot establish communication from custom client

[srgjc]

I would like to communicate with debugpy from a custom client I am building over tcp locally.
For this I run python -m debugpy --listen 5678 ./script.py. (with or without --wait-for-client does not make a difference)
When listening to this port I get this response:

Content-Length: 137

{"seq": 1, "type": "event", "event": "output", "body": {"category": "telemetry", "output": "ptvsd", "data": {"packageVersion": "1.8.8"}}}Content-Length: 139

{"seq": 2, "type": "event", "event": "output", "body": {"category": "telemetry", "output": "debugpy", "data": {"packageVersion": "1.8.8"}}}Content-Length: 189

{"seq": 3, "type": "event", "event": "debugpySockets", "body": {"sockets": [{"host": "127.0.0.1", "port": 5679, "internal": false}, {"host": "127.0.0.1", "port": 60323, "internal": true}]}}

Then I establish a connection to the port marked as internal and get the following request:

Content-Length: 168

{"seq": 1, "type": "request", "command": "pydevdAuthorize", "arguments": {"debugServerAccessToken": "76cec100048a7be9dc4f3195cefcf8d8687e56cde72ae065587cfc6ac659f1b4"}}

After looking at the source code I found how the json response should look like and sent this: (As for the token, I saw in the source it should match the server token, this might be wrong though...)

{"seq":"1","type":"response","request_seq":"1","success":true,"command":"pydevdAuthorize","body":{"clientAccessToken":"76cec100048a7be9dc4f3195cefcf8d8687e56cde72ae065587cfc6ac659f1b4"}}

After this I do not get a response.
Sending requests to the external ports also results in no reaction.
What is the correct way of establishing communication with debugpy?