An item cannot be ordered in one organization but works in another

The same item is orderable in one inventory organization and rejected in another.

The item is not assigned to that organization. Definition is master-level; availability is per organization.
Organization-level attributes differ. Customer-orderable, internal-orderable and transactable are set per organization and override what the master suggests.
The item's lifecycle phase or status disables ordering there. A status can permit stocking while disallowing ordering.
No valid item-organization sourcing rule exists. Without a source, the line cannot be fulfilled and is refused at entry.

Whether the item appears in the organization at all, before checking any attribute.
The orderable flags at organization level, compared against the organization where it works.
The item status and what that status permits.
Whether a sourcing rule and assignment set cover that organization.

If none of the above explains it, raise a ticket and include what you checked. Reading this article cost you no hours.