UNITYTLS_X509VERIFY_FLAG_NOT_TRUSTED issue troubleshooting

Description

Issue may happen for some users since 8.3.2 release because of two changes:

1. New Unity version more strict in certificate checks.
2. Let's Encrypt which we're using for SSL changed certification chain.

It happens to users who visited any of sites which uses Let's Encrypt certificates, but for some reason didn't have their certificates store refreshed.

Diagnosis (for Chrome)

You can visit https://play.eco and check certificate info.

If you see Let's Encrypt Authority X1 (deprecated) in the chain then you have to invalidate cert registry.

If you see Let's Encrypt Authority X3 then you have the valid chain.

How to fix

To fix this you need to reset cert cache (in elevated prompt):

1. certutil -setreg chain\ChainCacheResyncFiletime @now
2. certutil -urlcache * delete

You can find more details here.