Java Slack API: use of jetty libraries - jetty

Question

I'm following this Java example to post a message to a slack channel chat.postMessage/code. It uses these 3 lines referencing SlackAppServer:
import com.slack.api.bolt.jetty.SlackAppServer;
var server = new SlackAppServer(app);
server.start();
2 questions in regards to the use of SlackAppServer and com.slack.api.bolt.jetty:
Is the use SlackAppServer absolutely necessary for posting a message to a Slack channel using Java bolt libraries?
Library com.slack.api bolt-jetty makes use of the first 3 jetty libraries below that in turn rely on 3 more jetty libraries and on command "mvn spring-boot:run" produce the error below. Maven dependency tree doesn't show any overlapping libraries, but seems some type of incompatibility/conflict is taking place. Anyone else have seen this or similar errors?
jetty-servlet, jetty-server, jetty-webapp
jetty-alpn-server, http2-server, jetty-alpn-conscrypt-server
The errror:
Caused by: java.lang.IllegalAccessError: failed to access class org.eclipse.jetty.util.ArrayTernaryTrie from
class org.eclipse.jetty.http.PathMap (org.eclipse.jetty.util.ArrayTernaryTrie and org.eclipse.jetty.http.PathMap are in unnamed module of loader 'app')
at org.eclipse.jetty.http.PathMap.<init>(PathMap.java:96)
at org.eclipse.jetty.http.PathMap.<init>(PathMap.java:117)
at org.eclipse.jetty.http.PathMap.<init>(PathMap.java:107)
at org.eclipse.jetty.security.ConstraintSecurityHandler.<init>(ConstraintSecurityHandler.java:68)
... 25 more