The certificate is not signed by a trusted authority

My website uses a Let’s Encrypt certificate, which works fine in any browser, but starting from last month, The certificate is not signed by a trusted authority is displayed on the Android 6.0.1 browser. This is weird, it was displaying fine before and suddenly it has problems. For testing, I have another website, which also uses Let’s Encrypt’s certificate, but it displays fine on Android 6.0.1 browser without any security issues. This confuses me. They are both Let’s Encrypt certificates. Why can one website display normally but the other cannot? Can anyone help me? Thanks

Please fill out the fields below so we can help you better. Note: you must provide your domain name to get help. Domain names for issued certificates are all made public in Certificate Transparency logs (e.g. |, so withholding your domain name here does not increase secrecy, but only makes it harder for us to provide help.

My domain is:

My web server is (include version): Traefik 2.2.1

The operating system my web server runs on is (include version): Ubuntu 18.04

My hosting provider, if applicable, is: AWS

I can login to a root shell on my machine (yes or no, or I don't know): yes

I'm using a control panel to manage my site (no, or provide the name and version of the control panel): no

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Welcome @howiezhao

The site that fails is using the "short" certificate chain. The site that works has the normal long chain. There was an error on Nov13 when yintrust was renewed that caused this. Just renewing yintrust cert should fix that. You can see the cert that your site uses with a website like

Note the longer chain will be expiring and not available starting early next year. If you need to support older Android please follow the next link for instructions and guidance


Also see Long (default) and Short (alternate) Certificate Chains Explained


Thanks, guys, I updated the website certificate and it's working now. I read that article, so if we want to use Let’s Encrypt certificates on Android 6.0.1 next year, we will have to use Firefox Mobile? Will systems after Android 7.0 be unaffected?

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From September 30th, 2024 indeed.

Android 7.1.1 or higher. See:


While you probably do not control the Android devices used by your site's vistors, you might want to encourage any of your vistors that are using Android versions older than 11 to upgrade as they no longer receive security updates.


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