code: private void startRegistration() {
          //  Create a string map containing information about your service.
          Map<String, String> mRecordMap = new HashMap<>();
          mRecordMap.put(Configuration.PORT, Integer.toString(mPort));
          mRecordMap.put(Configuration.IDENTIFIER, myIdentifier);
  
          // Service information.  Pass it an instance name, service type
          // Configuration.SERVICE_REG_TYPE , and the map containing
          // information other devices will want once they connect to this one.
          WifiP2pDnsSdServiceInfo mInfo = WifiP2pDnsSdServiceInfo.newInstance(
                  Configuration.SERVICE_INSTANCE + myIdentifier,
                  Configuration.SERVICE_REG_TYPE, mRecordMap);
  
          // Add the local service, sending the service info, network channel,
          // and listener that will be used to indicate success or failure of
          // the request.
          mManager.addLocalService(mChannel, mInfo,
                  new CustomizableActionListener(
                          this.mContext,
                          TAG,
                          "Added Local Service",
                          null,
                          "Failed to add a service",
                          "Failed to add a service",
                          true)); //important: sets true to get detailed message when this method fails
  
      }
docs: Registers a local service.