How to fix org.telegram.telegrambots.meta.exceptions.TelegramApiRequestException: Error sending message: [404] Not Found?

Question

Java

I am completely new to the topic of developing telegram bots, and indeed in any kind of "programming"
And so, I want to write the first telegram bot that will be a Webhook (I more or less figured it out with LongPoling) ... I found, as expected, tutorials , video ... I did everything exactly ... But the author works, but I don’t ... And I don’t understand what’s the matter at all, since messages come to the program, and an exception pops up back:

org.telegram.telegrambots.meta.exceptions.TelegramApiRequestException: Error sending message: [404] Not Found
  at org.telegram.telegrambots.meta.api.methods.send.SendMessage.deserializeResponse(SendMessage.java:171)
  at org.telegram.telegrambots.meta.api.methods.send.SendMessage.deserializeResponse(SendMessage.java:24)
  at org.telegram.telegrambots.bots.DefaultAbsSender.sendApiMethod(DefaultAbsSender.java:725)
  at org.telegram.telegrambots.meta.bots.AbsSender.execute(AbsSender.java:47)
  at ru.ocs1c.help_ocs_bot.HelpOcsTelegramBot.onWebhookUpdateReceived(HelpOcsTelegramBot.java:39)
  at ru.ocs1c.help_ocs_bot.controller.WebHookController.onUpdateReceived(WebHookController.java:21)
  at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:64)
  at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.base/java.lang.reflect.Method.invoke(Method.java:564)

Well, and so on ......... how to be? my "supercode" is here https://github.com/SmithSE13/examples/tree/master/...
any information would be welcome! And it’s true that there’s no one to even ask, no one from the environment is trying to program.