Hi Abdul: The reordering rule looks at all the open MO/DO's in the system while creating the RFQ. As a result, one RFQ may be the result of shortages on more than one MO/DO. All products that are to be ordered from a supplier are clubbed into a single RFQ by Odoo to optimize the procurement process.

Reordering Rules will check required and available inventory, but there's no link between the demand and supply orders.

Replenish on Order / Make to Order (MTO) creates the supply (e.g. RFQ) and links it to the demand order (sales order or manufacturing order).

In Odoo 13, MTO will check the available inventory first, but this can be switched off (so it behaves the same way as Odoo 12 and creates the demand regardless of whether inventory is available).

Using Routes and Rules