How long is an invoice valid?

One hour. Pay within it if you can.

If a payment arrives after that, it is still honoured as long as the amount uniquely matches the invoice, within a reasonable time rather than indefinitely. If one of your two payments is missing, the email we send you names the exact deadline and the address the money goes to — that email is the authority on how long you have. The site picks it up by itself on its next check and your access opens then — just not the moment you pay, the way it does inside the hour.

A payment for a different amount, or one arriving after that time, does not open access by itself: see “I paid the wrong amount. What happens now?”