contractlinescheduleofvalue - invoice?

We found an issue where users are creating a record in the contractlinescheduleofvalue.

They then use this to create an invoice.

But then something happens and they do not post the invoice for several months.

So I have been asked that when an invoice is paid I go and check the date of the contractlinescheduleofvalue is within the same month as the invoice.

So far I have not been able to figure out the relationship coming from the invoice.

I am using kingswaysoft to do this update.

Can anyone help me out.

I am assuming I must be missing a table.

Thanks!!