Are you using Developers account with enterprice access to make custom object, If yes and still getting error in Api call then there would be error in the program you are writting, Please check Api call you are placing in right place. But here I would recommend you to use Private apps for api calls rather then Postman call, because it's easier than Postman. Reference articles Custom objects: https://developers.hubspot.com/docs/api/crm/crm-custom-objects Private apps: https://developers.hubspot.com/docs/api/private-apps