We handle this by splitting stock into two locations: one for POS (that's the original way odoo predicted to activr/offline/personal sales happen in odoo), one for Online (you can try running your site and connecting website to sales, or using sales by your employees or giving portal user to your customers, etc. ). Each channel reduces only its own location (inventory operations and route settings). Then a scheduled action (or connector if you use Shopify/WooCommerce) keeps both synced with the main warehouse. This way POS offline mode won’t double‑count, and you can track each channel cleanly. read and watch odoo's documentations and toturials for better examples.