If any of your sales are missing in the sales reports, check for the following:
Invoice Status: Check if the invoice of the missing sale item is open? If it's open, it'll not be reported as a sale. Zenoti usually considers only closed invoices as sales (unless your organization setting is to consider open invoices as well).
Payment Type: Check if the item was purchased using credits (memberships or packages) or redemptions (prepaid and gift cards). If yes, they will not reflect in the sales report. Only items purchased using Cash, Card, Check, and Custom Payments are reported in the sales reports.
Note: Items purchased using credits (memberships or packages) or redemptions (prepaid and gift cards) do not show up in Sales - Service or Sales - Product reports. They show up only in the Register Summary Report.