Why am I not getting a request token?


#1

I am trying to obtain a request token, but whenever I submit my request to POST api.twitter.com/oauth/request_token this is the answer:
"Failed to validate oauth signature and token"
I wonder what I am missing in the request header (BTW I am using Objective-c)
{ Authorization: OAuth oauth_callback=“http%3A%2F%2Fbytolution.com”,
oauth_nonce=“mmFdnKUKQLudIp68iEzwKTJ0lohVWYLFOqVYaeJcr9”,
oauth_signature_method=“HMAC-SHA1”,
oauth_timestamp=“1361823369”,
oauth_consumer_key=“XXXXXXXXXXXXXX”,
oauth_signature=“Kr/xhn7/FBvsOhDRL9pDPew9zP0=”,
oauth_version=“1.0” }

The signature is based on these parameters {
“http%3A%2F%2Fbytolution.com” = “oauth_callback”;
“oauth_consumer_key” = XXXXXXXXXXXXX;
“oauth_nonce” = 356KhF9zbVvePDUSGnOVzvvIe2njnCMUYJsbHLSf5y;
“oauth_signature_method” = “HMAC-SHA1”;
“oauth_timestamp” = 1361824020;
“oauth_version” = “1.0”;
}

And this is my signature base string: POST&https%3A%2F%2Ftwitter.com%2Foauth%2Frequest_token&http%253A%252F%252Fbytolution.com%3Doauth_callback%26oauth_consumer_key%3DXXXXXXXXXXXXX%26oauth_nonce%3D356KhF9zbVvePDUSGnOVzvvIe2njnCMUYJsbHLSf5y%26oauth_signature_method%3DHMAC-SHA1%26oauth_timestamp%3D1361824020%26oauth_version%3D1.0

Because I do not already have a token, my signing key is APPLICATION_SECRET& without a token.

WTF am I doing wrong???
Thanks in advance!