Posting possible solution that worked for me below.
I also had similar problem for 1 month +, tried to purchase from Web and Developer app, had "Purchasing failed" from both of the platforms.
I tried 2 different solutions for myself, so not sure which one eventually worked for me, but feel free to try both:
Solution 1: For some reason, on my iPhone settings -> click on your name -> Sign-in & Security, my phone number had warning next to it ("This phone number has to have SIM card ....."), not sure why, because i have SIM card on my phone. Fix was to enable iMessage in iPhone settings -> Messages, and enable iMessage.
Solution 2: Initially everywhere i tried to pay with Apple Pay (Wallet app), which always gave me an error "Purchasing failed", i tried removing ALL cards from my Wallet app, so i only had my default payment method left (Which you can add in iPhone settings -> click on your name -> Payment & Shipping), paying through that i finally got Success message.
Wishing you all good luck, hopefully one of the fixes mentioned in this 30+ pages thread will work for you.
I also have the same issue and have been trying for 5 months. I have called apple several times and went to my bank several times. The only thing I can do is find someone that has an account already and hope they don't put any virus in my code when its published.
Eu realmente nao entendo, porque uma empresa tao grande com um problema tao bobo. deveria no minimo ter uma documentacao explicando sobre o problema e como corrigir...
Hello! I'm also having trouble processing the credit card. I tried it with different cards from different brands. Apple, please improve this process. Any suggestions on how to solve my problem?