Error in call to API function "files/delete_v2": request body: could not decode input as JSON

hi, i'm trying to delete a file inside an app folder using HTTP POST request in UNITY,

i'm having no problem to delete file through the Dropbox API explorer,

but in UNITY receiving an error:

"Error in call to API function "files/delete_v2": request body: could not decode input as JSON"

here is the request form: 

URL: https://api.dropboxapi.com/2/files/delete_v2

headers:

'Authorization: Bearer my_super_secret_token'

'Content-Type: application/json'

'data: {"path":"/DEV_TEST1.mp4"}'

what am i doing wrong?