Cannot create new contact with custom attributes set via API

Hi all,

 I am working on a feature attempting to automate the creation of few contacts in our workspace by hitting the post endpoint for `{intercom_api_url}/contacts`.

My current data body looks like:

{
      email: providerData.providerEmail,
      name: providerData.providerName,
      phone: providerData.providerPhoneNumber,
      // These custom attributes throw an error in intercom when added.
         custom_attributes: {
           Is_provider: true,
           // provider_start_date: new Date().toDateString(),
         },
    }

Although the Is_provider custom attribute exists in the test workspace, my call keeps throwing me a 400 error with Bad Request.

Please help with understanding why this is happening and if possible a potential fix. This would allow us to onboard a lot more contacts very quickly.