Confluent Maven repository not working?

The file is available, since you can download it if you go to it directly: http://packages.confluent.io/maven/io/confluent/kafka-avro-serializer/3.1.1/kafka-avro-serializer-3.1.1.jar

You could try adding the -U flag to your maven command to force download of cached files.

The root of the repo isn't browsable which is why you are getting the message when browsing to http://packages.confluent.io/maven/

Needs to add confluent repositories in pom.xml
Please add below lines in the pom.xml

<repositories>
    <repository>
        <id>confluent</id>
        <url>https://packages.confluent.io/maven/</url>
    </repository>
</repositories>