Kayla Myers says she was partying with Soulja and co. at his Malibu home on Feb. 1, 2019 when she decided to leave at 2 AM. She admits her exit didn't go smoothly -- as she backed out, her car went off the driveway ... which pissed off one of Soulja's female assistants and sparked an argument between Kayla and the woman.

In her lawsuit, Kayla claims she was knocked to the ground, and then Soulja came over to kick her in the stomach and bash her in the head "with a large gun" -- and then told her she was going to die as he held the gun to her head.

According to docs, obtained by TMZ, she claims Soulja directed the assistant to drag Kayla to the garage, tie her up with duct tape and give her a shower. That sounds bizarre, but Kayla claims he wanted to clean her up from the ass-kicking she'd just suffered in the dirt outside the house.

Later, Kayla claims she was being held captive -- tied up with an extension cord -- in the garage when a male assistant offered to release her if she performed oral sex. In the suit, she says she felt she had no choice and did it. After that she was released at 8 AM ... she says with one final indignity -- Soulja allegedly said, "Now get this bitch outta here before I knock her down the stairs."

Kayla claims she suffered 3 fractured ribs and a bruised face. As we reported, she reported all of this to police, who conducted a raid at Soulja's house, where they found guns ... a probation violation. As you know, Soulja ended up doing time in L.A. County jail last summer.