If you are unable to access certain websites using HTTPS, the below steps should be taken:

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1. Check your internet connection is working properly. Check with your network administrator or ISP.
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2. Ensure that the website is using valid SSL certificates.
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3. Check the location of the website to verify you have access to it.
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4. Ensure that you are using the most updated browser version.
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5. Disable any anti-virus or 3rd party security software you are using
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6. Clear the cache, cookies, and browsing history.