For the sake of our fellow countrymen who will be visiting Qatar under Business Visa, I would like to clarify that there is no truth that the invitation letter needed to be authenticated in DFA. You should only have the following things before going to the Immigration for you to avoid being offloaded the plane:

1.) Your passport stamped by Qatar Embassy.
2.) Your round trip plane ticket.
3.) Pocket money of at least US$500 (at least PhP25,000).
4.) Your invitation letter from sponsor.
5.) Guts to prove the reason stated in your invitation letter. (tip: just tell the officer that you will go back on the date stated on your return flight). Relatively, people who are holding at least a college degree will experience lesser difficulty passing the immigration compared with those that are undergraduate or with no college education at all. Maybe you can make up with your work experience if you don't have a college degree.

Also, wear a decent and formal clothing. Just smile while you are being interviewed. Don't lose hope! Think that you can do it through the immigration!

Good luck my kababayans!