Unable to start live show from sessions page in new UI

[Tim020]

When trying to start a new session from the sessions tab in the new UI, the backend throws the following exception:

[E 260603 01:15:28 web:1966] Uncaught exception POST /api/v1/show/sessions/start (::1)
    HTTPServerRequest(protocol='http', host='localhost:8080', method='POST', uri='/api/v1/show/sessions/start', version='HTTP/1.1', remote_ip='::1')
    Traceback (most recent call last):
      File "/Users/tim/.pyenv/versions/venv313-digiscript/lib/python3.13/site-packages/tornado/web.py", line 1880, in _execute
        result = await result
                 ^^^^^^^^^^^^
      File "/Users/tim/Documents/Code/DigiScript/server/controllers/api/show/session/sessions.py", line 76, in post
        data = escape.json_decode(self.request.body)
      File "/Users/tim/.pyenv/versions/venv313-digiscript/lib/python3.13/site-packages/tornado/escape.py", line 104, in json_decode
        return json.loads(value)
               ~~~~~~~~~~^^^^^^^
      File "/Users/tim/.pyenv/versions/3.13.2/lib/python3.13/json/__init__.py", line 346, in loads
        return _default_decoder.decode(s)
               ~~~~~~~~~~~~~~~~~~~~~~~^^^
      File "/Users/tim/.pyenv/versions/3.13.2/lib/python3.13/json/decoder.py", line 345, in decode
        obj, end = self.raw_decode(s, idx=_w(s, 0).end())
                   ~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
      File "/Users/tim/.pyenv/versions/3.13.2/lib/python3.13/json/decoder.py", line 363, in raw_decode
        raise JSONDecodeError("Expecting value", s, err.value) from None
    json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)
[E 260603 01:15:28 web:2439] 500 POST /api/v1/show/sessions/start (::1) 13.43ms