Pending payments Query

I have built a property management app with a property table, payment table.

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property table has
Unit Number, Name, Phone and Email, rent etc
Payment table has
unit number, payment amount, payment type, month and year.
I linked both the table to unit number
I group all payments which are posted by year and month.

Now, I am working on finding the missing payment report for every month. I tried all options in appsheet. But i could not find a cross-reference query to generate a pending payments report.

Any helps is highly appreciated.

I understand, you should show existing records, not missing ones.
Why don’t you automate the periodic creation of “bills” on each month? Then, it would be much easier to match a payment with an existing bill, and show the bills not having a matching payment.