Within X days from due date / till the due date

we are issuing invoice as a company and in our templates we have:

In the event that the issued invoice is not paid within 7 days from the due date defined on the invoice, Supplier shall have the right...

OR

In the event that the issued invoice is not paid till due date defined on the invoice, Supplier shall have the right...

My understanding is that if it is period of more days, we should use "within" however if it is one exact day, we should use till due date and using this:

In the event that the issued invoice is not paid within due date

would be wrong.

Am I right?

Solution 1:

"The due date" suggests the last possible date that payment can be made (i.e. is due).

I would say either: in the event that the issued invoice is not payed by the due date defined on the invoice... (pay any time from now until the date specified)

or:

in the event that the issued invoice is not paid within 7 days from the date defined on the invoice... (pay any time in the week following the date specified).

If you use till/until, this suggests you don't want payment before the date specified: "please do not pay until the date specified on the invoice". This does not make clear whether you will accept payment after the specified date, however.