How to do error traversal?

Question

Delphi

if Http.HTTPMethod('POST','url') then
begin
if Pos('required',HTTP.Headers.Text)<>0 then
begin
Rez:=0;
end else
begin
Rez:=1;
end;
end else begin
error:=2;
end;
needed if error error:=2; return it for verification
how to do it