The API specification for the beta load accounts endpoint has been updated to include the x-www-form-urlencoded content type. An example cURL command using this new content type would be as follows:
curl -L 'https://sailpoint.api.identitynow.com/beta/sources/:id/load-accounts' \
-H 'Content-Type: application/x-www-form-urlencoded' \
-H 'Accept: application/json' \
-H 'Authorization: Bearer <TOKEN>' \
-d 'disableOptimization=true'