In the last few months something has changed so users are no longer redirected to PayPal after clicking the PayPal Express button on the product page.
I have a feeling it is to do with the patch SUPEE-9767 but I can't be certain.
I only say this because I have restored a backup to a test server and it is working on there correctly, the backup is from 4 months ago.
I see somebody else had a similar issue https://community.magento.com/t5/Payments-PayPal/Magento-Express-Paypal-Redirection-is-not-working/m... with no solution.
Is there anything I do to debug this issue? I'm familiar with PHP and most systems, but Magento just makes my mind melt, I can't make sense of what is happening here.
Any advice in debugging this would be greatly appreciated.