The front and back ends are separated in the project

The front end uses post request to send data to the back end, but there is an error:

Error: request failed with status code 500

We need to know that 500 represents (server internal error) the server encountered an error and was unable to complete the request.
Take a look at part of my original code:

Front end request:

Back end receiving entity and control layer code:

At this time, if you look carefully, you will find that the name of the parameter that my front-end carries when sending the request is   userName   and   password
However, the backend uses the user name when receiving the front-end parameters   and   Password, so I changed it   Front end   userName——> username

Finally OK!   If you also have this problem, you can check whether the parameters you send are consistent with those you receive, otherwise the parameters will be empty
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