When using Demand Planning module, the supply plans are created as per the demand thus projected.
If we have a Minimum Order quantity for placing purchase orders from a vendor, we have to do the following.
Suppose our supply plan suggests to procure 37 units every month to meet the projected demand

If the MOQ for that vendor is 80, then we can’t use this supply plan. So we have to update the item record.
Go to the Item Record, Choose the Fixed Lot Size as Lot Sizing Method and give the MOQ in the Fixed Lot Size.

Then rerun the supply plan.

The Supply plan got updated with MOQ.