Hi, I had the same issue , as while clicking on activate paypal express checkout in shopify it was redirecting me to paypal asking first login mail id -->again login mail id with passed --> you are almost done(here is the solution). Now you have two options 1 is to click on first button which will take you to paypal home page(that was my mistake). second to go to shopify home page -->re login now you can see it is activated now. done !!!
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