The match was made after Flair issued a challenge on tonight's SmackDown, which Bayley accepted, as seen below.
WWE Clash of Champions 2019 takes place on September 15 from the Spectrum Center in Charlotte, North Carolina. Below is the updated announced card:
SmackDown Women's Title Match
Charlotte Flair vs. Bayley (c)
King of the Ring Tournament Finals
TBD vs. TBD