Here's the answer:
“对不起”
(duì bù qǐ)
Watch a real native speaker say it:
Here's how it sounds in a textbook:
You could also say:
- duì-bù-qǐ
- duìbùqǐ
Fun fact: the hundreds of thousands of people learning Chinese with Memrise get this phrase correct 96.01% of the time!