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These quickbooks support staff don't even read our messages.

https://www.dropbox.com/scl/fi/isz3mjz8guwtqiwurx05i/AverageDayExample.xlsx?rlkey=8fvktm5xb5pg03bsfh...

The link provides a functional workbook for use with a slightly modified QuickBooks Online Invoices and Received Payments report.

Pick the date range for the report. More data points is typically better for averages to be meaningful. You may massage the data or clean it depending on your observations and needs.

You must modify the report to include the Customer field and move the field to the top of the report. Sample shown in the workbook.

You export the report to Excel, add filters, delete all rows where Date is "(Blanks)" and paste the non-blank rows into the Modified Report gray area. There are formulas to the left and right. The one on the left works to resolve sub-customers by splitting at the separating ":" if found. The one on the right calculates the number of days between Invoice and payment.

That data is then presented in the cross tab that shows the Average Days to Pay by Customer.