How can I get an invitation code?

Some companies are looking for testers with very specific demographics to test their products. So they bring their own testers to Userbrain by sending them an invitation code. Besides getting such a code sent from a company, there's no other way to receive an invitation code. 

Where can I enter my invitation code? 

Click on "I have an invitation code" at the bottom center of the screen. After putting in your invitation code, your email address, and your name you can start your test right away.

Do I get paid for my invitation test?

Userbrain won't pay you for taking an invitation test. The customer who is sending out the invitation code might offer a compensation for your time though.