Thanks for reaching out. During Site Kit set up users are requested for permission for Site Kit to pull information from users Search Console and other accounts. In some cases the boxes users need to tick may not all be selected, as per this screenshot. Can you attempt set up once more, and ensure all boxes are selected?
If you’ve already ensured all boxes are ticked, yet this same error appears, please attempt Site Kit set up this time from a Chrome browser incognito window and share whether you’re able to proceed.
Thanks so much James Osborne. That was exactly the solution!! Much appreciated!
Glad to hear it! If you have any further queries be sure to get in touch! Thank you