B2B Stripe Integration Error - Too many callouts exception

Hello,
I am having issues with the Stripe integration for my b2b site. I configured the payment gateway for stipe using the apex class(examples/b2b/checkout/payment-gateway-integration/Stripe/) and on the portal checkout flow when I click on submit payment button after entering the card details, seeing "too many callouts" exception. Please help me fix this issue.

Thanks in advance for your help.