I had that happen with them, when I first finally decided to trust their system to save my credit card information and turned on autorenew. Support told me it

I had that happen with them, when I first finally decided to trust their system to save my credit card information and turned on autorenew. Support told me it was/is because I have a couple of dollar balance with them from years and years ago, back when something involved making a transfer payment to my balance with them and then executing against that balance. If you have autorenew set, it first tries to draw against any existing positive balance you have directly with Namecheap. If/when that doesn't work, it then next tries your preferred payment method (e.g. your registered and designated preferred credit card). I was told if I found a way to clear my couple of buck balance with Namecheap, I'd no longer get the warning email. The first attempt would be against my credit card, which would work, and I'd just get one success email (after preceding "upcoming" emails and all that). I don't know whether this is correct. It's what I was told by support over chat, IIRC.