Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
If you are trying to use the CPro app on an iPhone or iPad (and Apple device) it need s to be mentioned that there appears to be a problem with the CPro app for craigslist management, since Apple c. roughly this August, took the CPro app down from the Apple store for unspecified reasons.
So I suspect that it is not the payment, but rather the app itself that is the problem.
To make sure the payment is not the problem (and that some bug in CPro is not, heaven forbid, siphoning money from your account) I advise you to independently verify that your credit balance is still good. Or that the balance you tried to buy, if it is not there, has not been paid for by money from your account yet (in case the buying of cP credits did not go through.)
Let me know what you find out, please.
I would advise you to try using the CPlus app for Craigslist... it is commented on (as of about early October of this year 2016) as a good alternative to CPro for Craigslist.