Spring WebFlux Netty SSL with self signed certificate error

I'm trying to access a Spring Boot application running on Netty via https in localhost using a self signed certificate on the server side.

Mine application.propertieslooks like this:

server.ssl.enabled=true
server.ssl.key-store-type=JKS
server.ssl.key-store=test.jks
server.ssl.key-store-password=password
server.ssl.key-alias=testkey

I have generated the keystore by:

keytool -genkeypair -alias testkey -keyalg RSA -keysize 4096 -keystore test.jks -validity 36500

I get the following error:

io.netty.handler.codec.DecoderException：javax.net.ssl.SSLHandshakeException：收到致命警报：io.netty.handler.codec上io.netty.handler.codec.ByteToMessageDecoder.callDecode（ByteToMessageDecoder.java:472）上的certificate_unknown io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead（AbstractChannelHandlerContext.java:374）上的io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead（AbstractChannelHandlerContext.java:360）上的.ByteToMessageDecoder.channelRead（ByteToMessageDecoder.java:278）

I've tried importing the certificate to the JDK truststore, and even to the OS, but still the same. One source suggested to name the key alias "testkey" to make it work, but that also didn't work. Since there is no other mention of this error in Google, I hope you can help.