If my oauthcallback contains query string
And when I do requesttoken I get following callback from ZenRep

Instead it should be "&oauthtoken=<Token>&oauthverifier=<verifier>". Since passed callback already contains "?state=

As per The OAuth 1.0 Protocol at https://tools.ietf.org/html/rfc5849
If the callback URI already includes a query component, the server
MUST append the OAuth parameters to the end of the existing query.