Here's how to correctly configure your example:

1. Enable Advanced Pricelist Features

• Go to: Sales → Configuration → Settings
• Enable:
  • ✅ Multiple Sales Prices per Product
  • ✅ Advanced price rules (discounts, formulas)

Click Save.

2. Configure the Pricelist

• Go to: Sales → Products → Pricelists
• Create or Edit a Pricelist (e.g., “Volume Discount – Product A”)

Click Add a Pricelist Item and configure like this:

✅ Entry 1 (for minimum 5 units):

• Applied On: Product
• Product: Product A
• Min Quantity: 5
• Compute Price: Fixed Price
• Fixed Price: 0

✅ Entry 2 (for minimum 10 units):

• Applied On: Product
• Product: Product A
• Min Quantity: 10
• Fixed Price: 10

✅ Entry 3 (for minimum 20 units):

• Applied On: Product
• Product: Product A
• Min Quantity: 20
• Fixed Price: 20

🧠 Important: Odoo applies the highest matching minimum quantity first. So order doesn't matter, but overlapping rules must not conflict.

3. Apply the Pricelist to the Customer or Sales Order

• Either:
  • Set the pricelist as default for the Customer (in the Contact form), or
  • Select the pricelist manually in the Sales Order before adding products.

✅ Example Behavior:

• Order 5 units of Product A → Price per unit = $0
• Order 10 units → Price per unit = $10
• Order 20 units → Price per unit = $20