API:Add Client

 $postfields["action"] = "addclient"; 
 $postfields["firstname"] = "Test";
 $postfields["lastname"] = "User";
 $postfields["companyname"] = "WHMCS";
 $postfields["email"] = "demo@whmcs.com";
 $postfields["address1"] = "123 Demo Street";
 $postfields["city"] = "Demo";
 $postfields["state"] = "Florida";
 $postfields["postcode"] = "AB123";
 $postfields["country"] = "US";
 $postfields["phonenumber"] = "123456789";
 $postfields["password2"] = "demo";
 $postfields["customfields"] = base64_encode(serialize(array("1"=>"Google")));
 $postfields["currency"] = "1";

 $command = "addclient";
 $adminuser = "admin";
 $values["firstname"] = "Test";
 $values["lastname"] = "User";
 $values["companyname"] = "WHMCS";
 $values["email"] = "demo@whmcs.com";
 $values["address1"] = "123 Demo Street";
 $values["city"] = "Demo";
 $values["state"] = "Florida";
 $values["postcode"] = "AB123";
 $values["country"] = "US";
 $values["phonenumber"] = "123456789";
 $values["password2"] = "demo";
 $values["customfields"] = base64_encode(serialize(array("1"=>"Google")));
 $values["currency"] = "1";
 
 $results = localAPI($command,$values,$adminuser);

result = success
message =  xxx - ID of the new user

result=error&message= You did not enter your first name# firstname field left blank.
result=error&message= You did not enter your last name# lastname field left blank.
result=error&message= You did not enter your email address# email field left blank.
result=error&message=The email address you entered was not valid # Invalid email address
result=error&message= You did not enter your email address# email field left blank.
result=error&message= You did not enter your  address line 1# address1 field left blank.
result=error&message= You did not enter your city# city field left blank.
result=error&message= You did not enter your state# state field left blank.
result=error&message= You did not enter your postcode# postcode field left blank.
result=error&message= You did not enter your country # country field left blank.
result=error&message= You did not enter your phone number# phonenumber field left blank.
result=error&message= Invalid telephone phone number# Invalid telephone format.