Sine-Liouville (SL) theory is a 2d string theory in a background with a tachyon condensate and has a dual description in terms of Matrix Quantum Mechanics. Using this description, almost 20 years ago instanton corrections to the partition function of SL theory have been found. However, this result left several puzzles and it was unclear how it can be reproduced using CFT technique. I reconsider this problem using recent insights about D-instantons in string theory, which allows both to resolve the puzzles and to match the instanton effects in the two formulations.