CORS error in redirecting to payment gateway

[upcoders]

Following errors occur when trying to redirect to payment gateway:

Access to XMLHttpRequest at 'https://www.paymentgateway.com/pg/StartPay/A00000000000000000000000000420755917' (redirected from 'http://127.0.0.1:8000/api/checkout') from origin 'http://127.0.0.1:8000' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

VM382:1 Uncaught SyntaxError: "undefined" is not valid JSON
    at JSON.parse (<anonymous>)
    at Object.error (api.combined.2829092665.admin.1.3.4.js:10649:43)
    at c (api.combined.2829092665.admin.1.3.4.js:570:28294)
    at Object.fireWith [as rejectWith] (api.combined.2829092665.admin.1.3.4.js:570:29039)
    at l (api.combined.2829092665.admin.1.3.4.js:570:79825)
    at XMLHttpRequest.<anonymous> (api.combined.2829092665.admin.1.3.4.js:570:82229)

api.combined.2829092665.admin.1.3.4.js:570 GET https://www.paymentgateway.com/pg/StartPay/A00000000000000000000000000420755917 net::ERR_FAILED

Payment gateway link is correct and opening it in new window works. How can I get rid of these errors? Thanks