How can we improve WHMCS?

We sell hosted phone solutions and have the following dilemma.

Our provider invoices us a month in advance.

We are provided a CSV file to enter data, which we do as recurring billable items each month on the 5th day of the month.

We enter our data to invoice on the 10th of each month with an invoice due date of the 25th.

In addition to the billable items, we have a product which also follows that invoice date and has some service fees attached.

The issue we have faced for years is that the product wished to have a date range of say 12/25/2021 - 1/25/2022. However, the provider has invoiced us for 12/1/2021 - 12/31/2021.

We get complaints all the time about this and have to explain.

The solution would then be to allow custom date ranges for certain products so that no matter what day they are set in invoice, for us this one invoices on the 10th day of each month, the date range could be stated to be all of the current month, the previous month, or the following month.

Hope this makes sense, would be a great help for us at least.