Why I get error with request to Google Identity Toolkit

I work with restAPI Identity Toolkit.

I get good response with request

POST https://identitytoolkit.googleapis.com/v1/accounts:sendOobCode

but there is a parameter ‘returnOobLink’ by default it’s false.
When I set it true to get OobCode for building my own custom request, I get error

{error:
    code: 400,
    message: 'INNSUFFICIENT_PERMISSION'
}

Which permission needs?