Try accessing the website from another browser, in case if there is an issue with the web browser you are currently using. If you are able to access the website from the other browser, then you may try fixing the current web browser.
Uninstall suspicious and malicious browser extensions
In most cases, the reason for the "You don't have authorization to view this page HTTP error 403" error message is a bad (sometimes even malicious) browser extension. To fix the issue, removing the browser extension is what you need to do. Sometimes, it's hard to tell which extension is causing the issue. To find out that extension, you can disable the extensions one by one and once you identify the right one, you can just remove it. Another indicator is the author's name - a suspicious author name can also reveal the bad extension (e.g. sadsadddx).
Contact the ISP (Internet Service Provider)
Another reason for this error can be the internet service provider you are using, as they, for some reason, don't let you access the website you want. To check this, verify that the website is actually running (e.g. via https://downforeveryoneorjustme.com). Then, connect to a different Wi-Fi network, or even mobile data and try visiting the website. If that works, contact the ISP support team and let them know of the issue.
Maybe the website you are trying to visit is currently unavailable, due to a server issue where the website is hosted. Hit the browser's reload button, several times a day, until the website becomes available.
Ensure that you have entered the website's URL address correctly
A typo in the URL address can cause the "You don't have authorization to view this page HTTP error 403" error message. The main reason is that most websites don't allow redirects, e.g. if you accidentally type https://facebook.com? you won't be redirected to https://facebook.com. Also, it is possible that the website you are trying to visit switched from http:// to https:// and the website's administrator forgot to apply a redirect.
Make sure to type carefully and double-check what you typed, to ensure that you won't run into this error.
Websites are like living beings and they constantly need to be updated. Maybe the person who was updating the website made a mistake, resulting in the "You don't have authorization to view this page HTTP error 403" error message. Surely, they would have fixed it immediately, however, they may not be aware of it, yet.
Contact the website's team and let them know of the issue, and they will fix it.
Check if you have entered the correct login details
Maybe you get the HTTP error 403 message because you have accidentally entered incorrect login details. Try to enter them again and in case if they are incorrect again, contact the website administrator.