Issues accepting payments?

[dcash]

I've recently had two customers whose card wouldn't process with the invoice sent.  CC is on for payments (as well as ACH but they didn't chose that.). I'm wondering if this is coincidence or if there is an issue. We only just started using square invoices and it was easier than what we were doing previously, but not if they can't actually pay!  We were able to accept payments for a few invoices before this issue started.