Unable to create index from c#

Elastic Stack Elasticsearch
1 
io.netty.handler.codec.DecoderException: javax.net.ssl.SSLHandshakeException: Received fatal alert: unknown_ca
        at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:480) ~[netty-codec-4.1.73.Final.jar:4.1.73.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:279) ~[netty-codec-4.1.73.Final.jar:4.1.73.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) [netty-transport-4.1.73.Final.jar:4.1.73.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) [netty-transport-4.1.73.Final.jar:4.1.73.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) [netty-transport-4.1.73.Final.jar:4.1.73.Final]
        at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410) [netty-transport-4.1.73.Final.jar:4.1.73.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) [netty-transport-4.1.73.Final.jar:4.1.73.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) [netty-transport-4.1.73.Final.jar:4.1.73.Final]
        at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919) [netty-transport-4.1.73.Final.jar:4.1.73.Final]
        at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:166) [netty-transport-4.1.73.Final.jar:4.1.73.Final]
        at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:722) [netty-transport-4.1.73.Final.jar:4.1.73.Final]
        at io.netty.channel.nio.NioEventLoop.processSelectedKeysPlain(NioEventLoop.java:623) [netty-transport-4.1.73.Final.jar:4.1.73.Final]
        at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:586) [netty-transport-4.1.73.Final.jar:4.1.73.Final]
        at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:496) [netty-transport-4.1.73.Final.jar:4.1.73.Final]
        at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:986) [netty-common-4.1.73.Final.jar:4.1.73.Final]
        at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) [netty-common-4.1.73.Final.jar:4.1.73.Final]
        at java.lang.Thread.run(Thread.java:833) [?:?]
Caused by: javax.net.ssl.SSLHandshakeException: Received fatal alert: unknown_ca
        at sun.security.ssl.Alert.createSSLException(Alert.java:131) ~[?:?]
        at sun.security.ssl.Alert.createSSLException(Alert.java:117) ~[?:?]
        at sun.security.ssl.TransportContext.fatal(TransportContext.java:358) ~[?:?]
        at sun.security.ssl.Alert$AlertConsumer.consume(Alert.java:293) ~[?:?]
        at sun.security.ssl.TransportContext.dispatch(TransportContext.java:204) ~[?:?]
        at sun.security.ssl.SSLTransport.decode(SSLTransport.java:172) ~[?:?]
        at sun.security.ssl.SSLEngineImpl.decode(SSLEngineImpl.java:736) ~[?:?]
        at sun.security.ssl.SSLEngineImpl.readRecord(SSLEngineImpl.java:691) ~[?:?]
        at sun.security.ssl.SSLEngineImpl.unwrap(SSLEngineImpl.java:506) ~[?:?]
        at sun.security.ssl.SSLEngineImpl.unwrap(SSLEngineImpl.java:482) ~[?:?]
        at javax.net.ssl.SSLEngine.unwrap(SSLEngine.java:679) ~[?:?]
        at io.netty.handler.ssl.SslHandler$SslEngineType$3.unwrap(SslHandler.java:295) ~[netty-handler-4.1.73.Final.jar:4.1.73.Final]
        at io.netty.handler.ssl.SslHandler.unwrap(SslHandler.java:1341) ~[netty-handler-4.1.73.Final.jar:4.1.73.Final]
        at io.netty.handler.ssl.SslHandler.decodeJdkCompatible(SslHandler.java:1234) ~[netty-handler-4.1.73.Final.jar:4.1.73.Final]
        at io.netty.handler.ssl.SslHandler.decode(SslHandler.java:1283) ~[netty-handler-4.1.73.Final.jar:4.1.73.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:510) ~[netty-codec-4.1.73.Final.jar:4.1.73.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:449) ~[netty-codec-4.1.73.Final.jar:4.1.73.Final]
        ... 16 more
2

Unfortunately posting part of a log, with no other information is unlikely to get you much assistance.

You've given no indication of what the code you have is doing, what version of Elasticsearch you are using, what your Elasticsearch config is, where this error is from.