Hello @Marco Spallone ,
This error means that there is something wrong when verifying server certificates. You could check if the server only has the wildcard certificate keychain or miss the certificate authority.
As the native Android document describes, Android typically trust only root CAs directly, which leaves a short gap of trust between the server certificate—signed by the intermediate CA—and the certificate verifier, which knows the root CA. To solve this, the server doesn't send the client only it's certificate during the SSL handshake, but a chain of certificates from the server CA through any intermediates necessary to reach a trusted root CA.
For more details, please refer to this doc: https://developer.android.com/training/articles/security-ssl
Best Regards,
Wenyan Zhang
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