How should I proceed in case of a payment failure?

You may try alternate payment methods highlighted in the links below in case of a payment failure. You can also check if your card is enabled for international transactions or use an alternate card. 

https://www.smergers.com/faq/how-do-i-pay-using-stripe/251/

https://www.smergers.com/faq/i-need-smergers-bank-account-details/250/