remove.bg's API at https://api.remove.bg/v1.0 removes image backgrounds. Point it at an image by URL with image_url; the response is the PNG itself (add -o out.png in curl). This is a multipart form — in PostTaco, the Body tab's Form mode.
Get a key at remove.bg and send it as the X-Api-Key header. In the examples it's written {{REMOVEBG_API_KEY}}.
Full reference: https://www.remove.bg/api
Example image from remove.bg's docs.
curl -X POST https://api.remove.bg/v1.0/removebg \
-H "X-Api-Key: {{REMOVEBG_API_KEY}}" \
-F image_url=https://www.remove.bg/example.jpg \
-F size=auto
curl https://api.remove.bg/v1.0/account \
-H "X-Api-Key: {{REMOVEBG_API_KEY}}"