This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 坆 is uncertain. It visually combines 土 (earth) and 攵 (a hand with a stick), but the original meaning and component relationship are unclear.
Since the meaning is unclear, focus on the shape: 土 (earth) beside 攵 (a hand holding a stick). Picture someone poking the earth with a stick, but remember that the actual meaning is uncertain.
For バイ, imagine buying a plot of earth (土) with a stick (攵) as a marker: buy -> バイ, though the kanji's meaning is uncertain.