I have been experiencing similar for months. Strange thing is I have two iMacs, and checkout works on one Safari browser, but not the other one. Very frustrating. But I got it to work today, finally, by the following: 1. log in to PayPal 2. in a separate window, log into the site I wanted to shop 3. At the top, click on "Safari" 4. In the drop down menu, click on "Settings for PayPal" 5. When the window pops up with the settings, make sure to UNCHECK "enable content blockers" Then do the same thing for the site you are shopping, making sure to UNCHECK "enable content blockers" This seems to fixed my months long issue of being unable to use the Safari browser with PayPal. Good luck!
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