Why is vk bot not working on heroku?

Question

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The situation is as follows:
I am making a bot for the VK group, the following modules are installed in the project:
- express io,
- body-parser,
- node-vk-bot-api I
use the Vkontakte Callback API to constantly support the bot.
The bot works successfully through ngrok, but for some reason it gives an application error on heroku and the VK server writes that my server returned the wrong answer.
At the same time, everything worked through the Long Polling API.
The token and confirmation are registered in the bot object.
UDP: issue resolved by changing port to process.env.PORT || 3000;