Upon checking error log , below is the error
[Wed Jul 07 16:20:43.901982 2021] [fcgid:warn] [pid 13014] [client 193.43.142.xxx:61463] mod_fcgid: stderr: Stripe Notice: Undefined property of Stripe\\Customer instance: sources, referer: https://www.temp.com/clients/creditcard.php
[Wed Jul 07 16:20:43.902000 2021] [fcgid:warn] [pid 13014] [client 193.43.142.xxx:61463] mod_fcgid: stderr: PHP Fatal error: Call to a member function jsonSerialize() on null in /home/temp/public_html/clients/modules/gateways/stripe.php on line 0, referer: https://www.temp.com/clients/creditcard.php
[Wed Jul 07 16:20:43.902002 2021] [fcgid:warn] [pid 13014] [client 193.43.142.xxx:61463] mod_fcgid: stderr: [WHMCS Application] ERROR: exception 'Whoops\\Exception\\ErrorException' with message 'Call to a member function jsonSerialize() on null' in /home/temp/public_html/clients/modules/gateways/stripe.php:0 Stack trace: #0 /home/temp/public_html/clients/vendor/whmcs/whmcs-foundation/lib/Utility/Error/Run.php(0): WHMCS\\Utility\\Error\\Run->handleError(1, 'Call to a membe...', '/home/temp...', 0) #1 [internal function]: WHMCS\\Utility\\Error\\Run->handleShutdown() #2 {main} {"exception":"[object] (Whoops\\\\Exception\\\\ErrorException(code: 1): Call to a member function jsonSerialize() on null at /home/temp/public_html/clients/modules/gateways/stripe.php:0)"} [], referer: https://www.temp.com/clients/creditcard.php