I use Add Funds on the PS5 console itself, but I've used the website too. The website just errors for me when I try to add funds there now, for some reason, but that seems to be affecting only me. The boost should work on both website and console, and it works for both adding funds to wallet and for checking out a cart of games.
Sounds like you did everything right.
How did you add via the console? Trying to find that option.
EDIT: Just found it under settings of the console and not in the PS Store on the console. Weird place for it to be but it worked. No errors at all.