Yes, in Odoo 18 (assuming you mean Odoo v15–v17 or an internal version labeled “18”), you can charge a customer for a recyclable item they bring in and increase your inventory weight — but you need to slightly adapt your process, because this scenario isn't directly standard.

You want to:

1. Charge the customer (issue a Sales Order or Invoice).
2. Increase inventory (receive goods, track weight).
3. Track this item by weight (e.g., kg/lb) instead of traditional quantity.

Even though the item comes from the customer, treat it like a reverse sale (buy-back) and use the following:

Create a Product for the Recycled Item

• Go to Inventory → Products → Create
• Name: e.g., "Scrap Metal – Customer"
• Type: Storable
• Unit of Measure: Weight-based (e.g., kg, lb)

Enable:

• ✅ "Can be Purchased" (to allow stock receipt)
• ✅ "Track Weight" (if using advanced tracking)

Create a Receipt (Manual or via Purchase)

Since the customer brings in the item:

• Go to Inventory → Operations → Receipts
• Receive the product manually
  • Vendor = Your customer (for tracking)
  • Product: Scrap Metal
  • Quantity: 25 kg (or whatever)
• Validate to increase stock

💡 Alternatively, create a Purchase Order from the customer as vendor if you want full tracking.