My credit also showed up today - pretty speedy for Kobo!
I have just now tried the same thing with my husband's account, and again, I had to try twice. I have now figured out, though, what I think is happening.
The first time when I hit the Visa Checkout button, it took me to the Visa Checkout sign-in pop-up window, I logged in (since he also has a pre-existing Visa Checkout account), and then it took me to the Kobo "buy" page. However, at the top, there was no card listed. So when I clicked on the green "complete purchase" button, it gave the same old error message.
Then I deleted the book out of the "buy" page, returned to Kobo home, and tried to buy the book again. This time, his credit card showed up at the top as a payment method, and, although there was nothing that I saw that indicated this was a Visa Checkout card, that's the only way it could have gotten there, since I had deleted out his other payment options before starting the process. And this time the sale went through.
This is the same procedure I followed with my account, although I didn't notice the absence or presence of a card listed at the top of the "buy" page when I did that one. And, as I said above, that account now has the $10 credit in it as of this morning.
So, it somehow seems to be connected to having to cycle through twice - maybe once to get logged in to Visa Checkout, and then a second time, so Kobo picks up the info and gets it into their system. Perhaps this only happens if you have a pre-existing Visa Checkout account, but in any case, this method has now worked twice, at least for the purchase of the book, in two different Kobo accounts, with two different Visa Checkout accounts.
My fingers are now crossed that my husband also gets the credit in his account - and I'll get to spend it
And karma to Purple Lady for the "do it twice" suggestion!