post
https://api.heymantle.com/v1/email/campaigns//deliver
Send an email campaign to a single customer. Use this for event-triggered or one-off emails where you want to target a specific customer.
Creates a delivery record and tracks opens/clicks like a normal campaign send.
If the campaign has allowRepeatDelivery: false, attempting to deliver
to the same customer twice will return a 409 Conflict error.
Rate limited to 100 delivers per minute per organization.