Investors had heightened expectations going into the quarter, and may have expected growth to be higher than reported, said DA Davidson & Co analyst Rishi Jaluria.
Slack's close competitor, Zoom Video Communications Inc, on Tuesday nearly doubled its expectations for annual sales as more people worked from home. Slack's platform, unlike Zoom's video focus, centers on messaging.
Jaluria added that billings are an important metric which investors view as a future indicator for the growth of companies like Slack, which have a subscription-based model.
Slack's first-quarter revenue rose 50% to $201.7 million (160 million pounds) from a year earlier, above analysts' average estimate of $188.1 million, according to IBES data from Refinitiv.
However, the workplace messaging company's total operating expenses in the first quarter jumped 63% to $252.2 million.
The economic damage brought on by the Covid-19 health crisis might also force companies to cut back on technology spending, Slack had warned in March.