VK API groups.setCallbackServer not working?

Question

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There is a method groups.setCallbackServer
Allows you to specify a server for CallbackAPI
My server returns the desired string.
When I manually set the URL through the group settings page in VK, everything works.
When I try to install the server programmatically, pulling the method, I get it all the time . Based on the method documentation, this means "the server returned an incorrect response." Does anyone know what is the reason? How to understand what exactly the server returns at this moment?
{"response":{"state_code":3,"state":"incorrect"}}

Answer 1

state_code=3, state="incorrect" — the server returned an invalid response.
Do you get the string that is the server confirmation from api ( https://vk.com/dev/groups.getCallbackConfirmationCode )? These lines are different for installation from api and from the VK interface.