Below is an outline of what sales statuses mean, and also how they are involved in the sales process.
When a sale is created, is has a status OPEN, but that status is not stored on the server. Once a sale is saved to the server is becomes SAVED, and that's the status you should be using if you're trying to create a parked sale.
Note: A parked/SAVED sale doesn't change stock count and doesn't have to have any payments associated with it.
There are three basic types of sales, Regular, on-account and layby:
For a regular sale the customer_id is optional. If VEND doesn't receive an ID for a customer to assign the sale to, it will use a default customer, named 'walk-in'. A regular sale can either be posted as CLOSED (when the payment total is equal to the sale total), or as SAVED (where it will be parked and made available for retrieval in the sell screen).
A similar logic applies to on-account sales. Until paid in full they should be visible as ONACCOUNT. Once paid in full the status should change to ONACCOUNT_CLOSED. For an on-account sale, the goods leave the store before the sale is paid in full.
Until paid in full the sale status should be visible as LAYBY. Once paid in full, the status should change to LAYBY_CLOSED. A LAYBY is a sale where the customer pays for the goods in a few installments, but only receives the goods once the sale is paid in full.
For all sales the status can also be changed to VOIDED in order to void a sale, which will return sale items into the stock and reduce the loyalty balance for the customer. Once a sale is VOIDED the status should never be changed to anything else.
Below are some articles on VEND related to this topic:
Layby sales in VEND
Making your first sale in VEND
VEND's sell screen