post https://api.prtmb.com/api/v2/audience-members/me/checkouts//complete-sync
Complete the checkout process on a cart resource owned by the current audience_member synchronously.
IMPORTANT: ensure client timeout is long enough to wait for response.
This request may take longer than 3-5 seconds to complete. Ensure that the client does not timeout
the request early to avoid false timeout errors.
Callback