Here's the Paypal security updates that go into effect in June - https://www.paypal-knowledge.com. If you don't make these changes you may no longer be able to connect to and process Paypal payments.
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SSL Certificate Upgrade
Make sure the SSL for your website has been upgraded to SHA-256. Go to https://shaaaaaaaaaaaaa.com/ to check. If you don't have an SHA-256 SSL, contact your web host to get an upgrade.
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Disable TLS 1.0 and 1.1
Go to https://www.ssllabs.com/ to see if you're web server supports TLS 1.0/1.1. If it does, talk to your web host about updating your server. Both of these need to be turned off.
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Paypal Standard - IPN verification postback requires https
If you're using Paypal Standard, login to your Paypal account, got to Profile > Profile and Settings > My Selling Tools > Website Preferences, and make sure your Return URL begins with HTTPS
