Getting 404 When Creating Campaign

Having some issues when posting a new campaign via the API.

Posting to: https://backstage.taboola.com/backstage/api/1.0/{account_id}/campaigns/

So the account_id we are using has some pre-existing campaigns in it. I am able to fetch account info via the API. Using PHP for posting a campaign though results in a 404. I have tried just using the example vars from the API, but I get the same result.

PHP:
curl_setopt($ch, CURLOPT_POSTFIELDS, "{"name":"DemoCampaign","branding_text":"Pizza","cpc":0.25,"spending_limit":1000,"spending_limit_model":"MONTHLY","marketing_objective":"DRIVE_WEBSITE_TRAFFIC"}");