Bugs in fuzz json packets

[Min9-sec]

Hello, I have a bug in the process of using arjun. I need to perform fuzz parameters in the position of $arjun$in the packet below, and my username and password must be added

I tested this by entering the following command on the command line

I checked the fuzz packets sent by arjun through packet capture, and found the following result. I would like to ask whether it is an incorrect use method or a bug in the program