Online shop not wanting to take my money

I went to the shop this morning to order some water leak detectors to add to my system. Put them in the cart, pick my shipping preference, and go to put the payment info in. Because my saved credit card has been replaced with a new expiration date and CCV, I decide to add a new card. When I submit the payment, the page just says "Loading…" and spins and spins and spins. 

OK, maybe it's a Safari on the Mac issue (which, IMHO, shouldn't be an issue at all). So I go to Firefox, go through the same process. When I submit the payment, I get a cryptic message that seems to say the credit card submission failed. 

I don't know where else to report that there's obviously some kind of bug in the web shop that the company may want to fix (at least if they want to get a bit of coin from me).

Sorry if I seem irritated, but I am. I've been very happy with SimpliSafe, even added a video doorbell and outdoor camera earlier this summer. But now this issue is completely getting in the way. I just hope someone from SimpliSafe reads this forum and can report this issue to the right people.