Be aware that fake credit card numbers should not be used in an attempt to pay for goods and services because it constitutes fraud, and you can be subject to criminal charges. In case an online merchant specifies that they will charge a registration fee, using a fake card can be deemed illegal in the eyes of the law.
Do fake credit cards actually work?
The verification test that credit cards must pass uses the Luhn Algorithm to establish whether their number is correct. That is why even the fake card numbers can pass the validity test. The financial transaction is an entirely different process, and fake credit cards cannot be used to purchase goods or services.