PayPal's Notify_url can't come back

PayPal's notify_url cannot be returned
After the payment is successful, PayPal does not return to the specified notify_url, so I do not know if the payment was successful.
Please be a big help to see where the problem is.
If you have PayPal's sandbox account, you can change your business account and put the URL in the browser.
Https://www.sandbox.paypal.com/cgi-bin/webscr?cmd=_cart&upload=1&charset=utf-8&currency_code=HKD &business=jxsrsxyx%40163.com&return=http%3a%2f%2fwww.custom888.com%2findex.php%2forder%2fview_case_ Order%3fcod_status%3d0&notify_url=http%3a%2f%2fwww.custom888.com%2fapps%2fpaypal%2freturn_url.php&item _number_1=1-5&item_name_1=00000000005&amount_1=50.00&quantity_1=1

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Tomorrow should have PayPal salesman contact you. I haven't done PayPal, I don't know.
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See if your firewall is in effect?
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Paid for, worth paying attention to
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Let me tell you something. First: You have to have a public network IP, not an intranet
Second: Directly with the production environment testing, no sandbox, the same PayPal code, in the sandbox I will not be notified, in the production environment. You change the amount to 0.01 test.
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Direct website testing, do not use the public network. Submit address is: HTTPS://WWW.PAYPAL.COM/CGI-BIN/WEBSCR

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