Issue with removing background and transparancy

I’m using the background removal API and I want the output image to have transparent background but I receive some weird gradient for the background. When I try the same call with a white background everything is OK. Following is the command I use to call the API and 3 images. The input one. The output with white background and the output with transparent background.

curl --request POST
–url https://sdk.photoroom.com/v1/segment
–header ‘Accept: image/png, application/json’
–header ‘Content-Type: multipart/form-data’
–header ‘x-api-key: [MY_API_KEY]’
–form image_file=@/home/igov/input.jpg
–form format=png
–form bg_color=#00000000
–form channels=rgba
-o output.png