Blac Chyna's gotta write a fat check to her former landlord for allegedly bailing on her lease and not paying rent ... because she didn't even bother to fight the lawsuit against her.
According to new legal docs obtained by TMZ ... BC's been ordered to fork over nearly $72,000 to Michael Kremerman, who sued her for unpaid rent and damages to the rental home.
It's a default judgment, meaning the judge ruled for Kremerman because Chyna never responded to the suit.
As we first reported ... the landlord filed suit against Blac Chyna back in April, claiming she bolted on her lease 5 months early, didn't pay a dime after leaving and removed fixtures and equipment from the pad.
The landlord said BC was $48,546 in the red, and he sued for that amount plus interest and attorney's fees ... hence the $72k judgment.
The expensive lesson here for Chyna -- no such thing as free rent.