Invoice sent! But then can’t pay!?

For some reason, invoice won’t let you pay sometimes… And I have no idea why it works sometime, it doesn’t other time… for those customers tried and didn’t work, I am so sorry for the inconvenience! I guess second time is a charm usually, I resend it then it works for most of time…. But then if the second time doesn’t work, please let me know ASAP. The payment failure notice won’t give me notification. I have to check back to the admin time to time. So it is better to let me know that your payment trial didn’t work…