Chatbot - Panel KeyError

can someone tell me what is the reason for this error?

python --version
Python 3.12.3

panel --version
1.4.3

jupyter --version
Selected Jupyter core packages…
IPython : 8.24.0
ipykernel : 6.29.4
ipywidgets : 8.1.2
jupyter_client : 8.6.2
jupyter_core : 5.7.2
jupyter_server : 2.14.0
jupyterlab : 4.2.1
nbclient : 0.10.0
nbconvert : 7.16.4
nbformat : 5.10.4
notebook : 7.2.0
qtconsole : 5.5.2
traitlets : 5.14.3