Try this: Go to go google type "paypal account settings" press enter, in the first option that shows copy the link then enter that same first option, login like usual, in here should appear the phone number authentication screen, paste the link earlier and press enter while on this same page, do not exit the phone number authentication page and then paste the link this is important, after this should appear your paypal account settings where you can change your phone number and solve your problem. If this still doesnt work for you try in a diferent browser, i used Chrome for this. If it still gives you same error i advise you to try later as it can really be a issue in paypal end.
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