Gigi Gorgeous, a transgender model and Kylie Jenner's BFF, is being detained at the Dubai airport because she used to be a man.

Gigi, who became famous for documenting her transition on social media, tells TMZ she was stopped at Immigration. She says the immigration officer said, "I was told you are transgender. You cannot come into the country."

Gigi was born Gregory Lazzarato, but says her passport has been updated since she transitioned ... it now reads "Gigi Loren."

Airport police have a different story. They say the passport describes her as male and the passport photo shows Gigi as a male. Gigi tells us that's simply not true.

We did some checking ... in Dubai the "imitation of women by men" is illegal, and violators face up to a year in jail.

She says they still have her passport, and she's trying to get out of the country.