I'm facing the same issue.

Error invoking registration handler for application "/ccm" at https://localhost:9443/ccm/service/com.ibm.team.repository.service.internal.setup.IRegistrationHandlerServiceID CRJAZ1720E
com.ibm.team.repository.common.TeamRepositoryException
com.ibm.team.repository.service.internal.discovery.ApplicationRegistrationFriendRestService.postRegisterApp(ApplicationRegistrationFriendRestService.java:142)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:79)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:618)
org.eclipse.soda.sat.core.internal.record.ExportProxyServiceRecord.invoke(ExportProxyServiceRecord.java:370)
org.eclipse.soda.sat.core.internal.record.ExportProxyServiceRecord.access$0(ExportProxyServiceRecord.java:356)
org.eclipse.soda.sat.core.internal.record.ExportProxyServiceRecord$ExportedServiceInvocationHandler.invoke(ExportProxyServiceRecord.java:56)
$Proxy293.postRegisterApp(Unknown Source)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:79)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:618)
com.ibm.team.repository.servlet.AbstractTeamServerServlet.doModelledRestService(AbstractTeamServerServlet.java:501)
com.ibm.team.repository.servlet.AbstractTeamServerServlet.handleRequest2(AbstractTeamServerServlet.java:1832)
com.ibm.team.repository.servlet.AbstractTeamServerServlet.handleRequest(AbstractTeamServerServlet.java:1688)
com.ibm.team.repository.servlet.AbstractTeamServerServlet.service(AbstractTeamServerServlet.java:1598)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.eclipse.equinox.http.registry.internal.ServletManager$ServletWrapper.service(ServletManager.java:180)
org.eclipse.equinox.http.servlet.internal.ServletRegistration.handleRequest(ServletRegistration.java:90)
org.eclipse.equinox.http.servlet.internal.ProxyServlet.processAlias(ProxyServlet.java:111)
org.eclipse.equinox.http.servlet.internal.ProxyServlet.service(ProxyServlet.java:75)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.eclipse.equinox.servletbridge.BridgeServlet.service(BridgeServlet.java:120)
com.ibm.team.repository.server.servletbridge.JazzServlet.service(JazzServlet.java:62)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:172)
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:563)
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
org.apache.catalina.authenticator.SingleSignOn.invoke(SingleSignOn.java:420)
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:174)
org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:879)
org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665)
org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528)
org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81)
org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:689)
java.lang.Thread.run(Thread.java:811)
Caused by:
Registration handler for application "/ccm" at https://localhost:9443/ccm/service/com.ibm.team.repository.service.internal.setup.IRegistrationHandlerService failed with status 400 and response body "{"errorTraceMarshall":,"errorCode":400,"nestedError":{"errorTraceMarshall":,"errorCode":null,"errorTrace":,"errorClass":"com.ibm.team.jfs.app.http.HttpInternalServerErrorException","errorMessage":"Request to service https:\/\/saar-laptop:9443\/jts\/base\/service\/com.ibm.team.repository.service.internal.discovery.IFriendsAdminRestService\/friends?includeInternal=true failed with status code 404 and response body </title>ID CRJAZ1721E
com.ibm.team.repository.service.internal.discovery.ApplicationRegistrationFriendRestService.notifyAppRegistrationHandler(ApplicationRegistrationFriendRestService.java:213)
com.ibm.team.repository.service.internal.discovery.ApplicationRegistrationFriendRestService.postRegisterApp(ApplicationRegistrationFriendRestService.java:131)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:79)
... 39 more

my application settings are as follow:
Add Application
Property

Value
Application Name: /ccm
Discovery URL: https://localhost:9443/ccm/scr
Application Type: Unknown
Consumer Secret:
Re-type Secret:
Functional User ID: saar

That appears to be a different issue (you're not getting UnknownHostException). It appears that the root cause of your problem is

Request to service https:\/\/saar-laptop:9443\/jts\/base\/service\/com.ibm.team.repository.service.internal.discovery.IFriendsAdminRestService\/friends?includeInternal=true failed with status code 404

and the URL doesn't look right - there is no such thing as "/jts/base". Could you have set the public URI property for the JTS to https://saar-laptop:9443/jts/base? It should be just https://saar-laptop:9443/jts.

Has someone a answer to the first post?