Hello - You can try to filter by "last invoice date", this field will be the closest available that you give you a sign of inactivity.

That is something that would work perfectly but it doesn't seem like its an option for me in the version that we have. is there an update or anything that you know about? or a way that i'm missing the search term somewhere?

I have tried that option on the current version and it does not yield any results either. Use the export function under File to achieve the same results. when prompted as to which fields to export, specify Customer#, Name and last invoice date. Once the spreadsheet is created, sort by dates and there you are.