Upload to the Box with ADF

I cannot upload to the Box by calling API in the Azure Data Factory.
I can not use SDK and I got HTTP 400 error ,
“Malformed stream”
following is the Body that I created in the Azure pipeline:( it should be in JSON format)

@concat('--------------------------9fd09388d840fef1
content-disposition: form-data; name=“attributes”

{“name”:“testdev.xlsx”, “parent”:{“id”:“0”}}
--------------------------9fd09388d840fef1
content-disposition: form-data; name=“file”; filename=“testdev.xlsx”
content-type: text/csv

‘, variables(‘varFileContents’),’

--------------------------9fd09388d840fef1–
')