Can help ?
[00:05:46] [Craft Scheduler Thread - 2/WARN]:
javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.security.ssl.Alerts.getSSLException(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.security.ssl.SSLSocketImpl.fatal(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.security.ssl.Handshaker.fatalSE(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.security.ssl.Handshaker.fatalSE(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.security.ssl.ClientHandshaker.serverCertificate(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.security.ssl.ClientHandshaker.processMessage(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.security.ssl.Handshaker.processLoop(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.security.ssl.Handshaker.process_record(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.security.ssl.SSLSocketImpl.readRecord(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.security.ssl.SSLSocketImpl.performInitialHandshake(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.security.ssl.SSLSocketImpl.startHandshake(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.security.ssl.SSLSocketImpl.startHandshake(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.net.
www.protocol.https.HttpsClient.afterConnect(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.net.
www.protocol.https.AbstractDelegateHttpsURLConnection.connect(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.net.
www.protocol.http.HttpURLConnection.getInputStream0(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.net.
www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.net.
www.protocol.https.HttpsURLConnectionImpl.getInputStream(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at com.iridium.iridiumskyblock.IridiumSkyblock.lambda$getLanguages$2(IridiumSkyblock.java:280)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at com.iridium.iridiumskyblock.IridiumSkyblock$$Lambda$3792/1269574172.run(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at org.bukkit.craftbukkit.v1_16_R1.scheduler.CraftTask.run(CraftTask.java:81)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at org.bukkit.craftbukkit.v1_16_R1.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:54)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at java.lang.Thread.run(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: Caused by: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.security.validator.PKIXValidator.doBuild(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.security.validator.PKIXValidator.engineValidate(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.security.validator.Validator.validate(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.security.ssl.X509TrustManagerImpl.validate(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.security.ssl.X509TrustManagerImpl.checkTrusted(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: ... 20 more
[00:05:46] [Craft Scheduler Thread - 2/WARN]: Caused by: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.security.provider.certpath.SunCertPathBuilder.build(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at sun.security.provider.certpath.SunCertPathBuilder.engineBuild(Unknown Source)
[00:05:46] [Craft Scheduler Thread - 2/WARN]: at java.security.cert.CertPathBuilder.build(Unknown Source)