She added, "I’ll be back better and stronger soon. Don’t Worry.”
The 32-year-old New York native gave no details on her condition.
Cardi gave birth to her third child with rapper Offset less than two months ago. The two are going through a divorce.
She was to have performed along with Earth, Wind & Fire, Nelly, Gunna and GloRilla at the two-day ONE Music Fest.