When you create a contact in Pooltrackr, they will be immediately created in Lightspeed.
When you create an invoice in Pooltrackr, the invoice will be sent immediately to Lightspeed and Xero, with all line items. The invoice will be assigned to the linked contact, meaning you can take payment from Lightspeed or Xero.
Pooltrackr reads products from Lightspeed so any changes are automatically reflected in-field. And it means that inventory is automatically adjusted as service invoices are generated.