As this article describes, there are different inventory statuses for products that can be seen when you goto that products' detail page.

Products have active and available inventory based on the statuses of their packages. A product's active inventory is the sum of all the active packages it has.

Packages are first active when you import them from Metrc or if you create them using assemblies / splitting packaged in Distru. A product's active inventory is calculated by adding all the active packages that belong to it. Whatever is active in Distru should also be active in Metrc (as in found in the Packages > Active tab). If not, please contact us to fix this. 

If added to a sales order, the package's status becomes selling, and the active inventory of that package is subtracted from the active inventory of the product it belongs to, thus lowering the active inventory of that product. Packages also have other status which we describe in the article shared above.

If you create a sales order with the 'processing' status without assigning a package, its inventory of the product added becomes reserved and no longer available until you match that sales order to an outgoing transfer (or assign a package to that sales order). 

When something is reserved, the available inventory goes down, because reserved + available = active inventory. The only way to increase available inventory of a product is to either get more active inventory or to lessen the reserved amount but matching the sales order to a transfer or by assigning packages to the product (line item) in a sales order.