TP link extender cannot access the Internet

I recently upgraded to the new Xfinity equipment, XB8. I then upgraded my extender to take advantage of The new  router with a  TP-link RE 315. The connection between the router and the extender looks perfect. However, I cannot access the Internet through the extender. It looks green initially, but when I try to do something,  for example, do a speed test-it says it can’t access the Internet and turns red. I tried it with the advanced security on the Xfinity router turned off and that did not help. Any assistance would be welcomed. Thank you in advance.