Re: Why isn't my $75 voucher from wix.com showing up on my account?
If you have already set-up your billing information and entered the voucher in your new AdWords account you will see the credit after "X" amount of dollars are spent.
Usually there is a fulfilment requirement to use the voucher, usually $25. So you have to use $25 of your own ad spend and then the $75 is credited to your account. More details on this at Google Voucher Support. If you don't see the credit appear after you fulfill the requirement mentioned in the offer, it's probably wise to give AdWords a call.
I hope this is helpful. Good luck with your new campaign!
Stefan T. Martinez
-- Not an AdWords expert, just a student eager to learn more...