PubMatic falls after Q3 revenue forecast below estimates

** Ad tech firm PubMatic's PUBM.O shares fall 22.8% to $8.16 in extended trading

** PUBM forecasts Q3 revenue to be between $61 million and $66 million, compared with analysts' average estimate of $70.6 million, according to data compiled by LSEG

** "While our outlook includes a reduction in ad spend from one of our top DSP (demand-side platform) partners, the underlying health of the business remains strong while we mitigate the impact," CFO Steve Pantelick says

** Revenue up 6% at $71.1 million for Q2, beating est of $67.9 million

** As of last close, stock down ~28% this year