We are using the API AppliedDocsListGet_API. One of the returned values refers to AdjType 400, which is absent in the documentation. What does it mean?
The parameter will be added to the documentation in scope of the doc bug #DOC-328 ("Update status of AdjType in Applied DocsList_API") fix.
400 means "Link".
The link is something the document was initially created for. For example, the payment was created to pay an order with id 123. The API call will return this order id with the AdjType 400. This link will be left forever, even if you later detach the payment from this order (e.g. in case order provisioning fails). For invoice there may be a link to the payment, if the payment was created for this specific invoice (e.g. in situations when provisioning is before payment, we pay not order, but invoice). The same when you do the call for the order - if order was payed with the payment, the link to this payment document will exist.
Adjustment is valid for documents - when something is attached, and adjusts the balance accordingly. Reference is when the order is referenced to invoice or vise-versa.