In Acumatica, the "Mark for PO" function on the Sales Order form is designed to allow users to create linked Purchase Orders based on the quantities listed on the Sales Order lines. However, by default, the system typically creates Purchase Orders for the full quantity mentioned in the Sales Order line.

To create a Purchase Order for less than the full quantity, you can use the following approaches:

 1. Manual Adjustment During Purchase Order Creation
   After using the "Mark for PO" function on the Sales Order:
   - Navigate to the Purchase Order that is created.
   - Manually adjust the quantity of each line item on the Purchase Order to reflect the quantity you actually want to order.
   - This will still keep the Purchase Order linked to the original Sales Order, but for the reduced quantity.

2. Splitting the Sales Order Line
   Another option is to split the Sales Order line before using the "Mark for PO" function. You can manually split the Sales Order line into multiple lines with different quantities. This allows you to:
   - Use "Mark for PO" on one of the lines for the reduced quantity.
   - The remaining quantity will stay on the Sales Order without being marked for PO, so you can manage it later as needed.

3. Use of Partial Purchase Order Release
   After marking the line for Purchase Order, Acumatica allows you to manage partial quantities. You can:
   - Create the Purchase Order with the full quantity but later receive partial quantities or process partial shipments.
   - This helps in cases where you only want to order a part of the quantity now and the rest later.

4. Custom Workflow
   If your business frequently needs to order quantities that are less than what's mentioned on the Sales Order, you can consider a custom workflow or automation. This can help prompt users to specify the exact quantity to be included in the Purchase Order when using the "Mark for PO” function.