curl --request POST \
  --url https://billing.funnelfox.com/{org_id}/v1/user/update_email \
  --header 'Content-Type: application/json' \
  --header 'ff-secret-key: <api-key>' \
  --data '
{
  "external_id": "<string>",
  "email_address": "jsmith@example.com"
}
'

{}