Paypal subscription (We are not getting response from paypal in success or cancel url. )

[dateReady]

Hello,
We are using button code by following steps in url (https://www.paypal.com/us/brc/article/how-to-add-subscription-payments-button-to-website) and for response code, we use code defined in this url(https://www.codexworld.com/paypal-subscriptions-payment-gateway-integration-php).  But we didn't get a response after successful payment both in Sandbox and Live methods.
 Issue -  We are not getting a response from PayPal in the success or cancel URL. 

Our demo URL - https://www.dateready.com.au/dr/?user_id=MQ== (sandbox) It always shows INVALID in the success URL, after filling in all details correctly.

Regards,
Arun Gupta