I understand you are having trouble while using MATLAB on jupyter notebook. 
The response code you mentioned "Error code 500 " it indicates that there is an internal server error. This error can occur due to various reasons, such as connectivity issues, server misconfiguration, or package installation conflicts. 
Here are a few steps you can try to resolve the issue: 
- Retry the installation: Sometimes, the error can be temporary. Retry the installation after few hours using below command: 
 
    python -m pip install jupyter-matlab-proxy  
- Check internet connectivity: Ensure that you have a stable internet connection. If you are behind a proxy or firewall, make sure the necessary settings are configured to allow the package installation. 
 - Upgrade ‘pip’: Update your pip package manager to the latest version by running the following command: 
 
    python -m pip install --upgrade pip 
- Clear ‘pip’ cache: Clear the pip cache to eliminate any potential conflicts by running the following command: 
 
    python -m pip cache purge 
 
I hope this information resolves your query. If still you face the same error you can raise an issue on github.