@kanha141, did you get this figured out? We are running into the same issue. Our creds appear correct as we tested the process manually with python and postman.
I see the note in the SailPoint documentation about 256-bit encryption (which Box requires) and needing JCE for the JRE, but that is where I got lost in replacing the jars in the JRE. I didn’t know if this was on the IDN side/possible in IDN.