what is mean by prefilght request and how to stop that?

hi guys if anyone know this , please help me , i have login form which has this funtion , and also i have a backend server running on different port , which send the jwt token to the front end , but what the issue is when i click the button in frontend , i make preflight request , thats why i cannot able to access the token in frond end ,

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I just want to access the jwt token which send from the server, and also why please expalin why this preflight request was made every time i click the button , is there way to avoid these req