code: public void doSendSticker(@NotNull Peer peer,
                                @NotNull Sticker sticker) {
  
          long rid = RandomUtils.nextRid();
          long date = createPendingDate();
          long sortDate = date + 365 * 24 * 60 * 60 * 1000L;
  
          StickerContent content = StickerContent.create(sticker);
  
          Message message = new Message(rid, sortDate, date, myUid(), MessageState.PENDING, content);
          context().getMessagesModule().getRouter().onOutgoingMessage(peer, message);
  
          pendingMessages.getPendingMessages().add(new PendingMessage(peer, rid, content));
          savePending();
  
          performSendContent(peer, rid, content);
      }
docs: Sending sticker