Luce Bri is a human fighter, who decided to take the Martial Artist archetype dedication.
This means Luce doesn't have access to Flurry of Blows, as it's only available if Luce instead takes the Monk multiclass dedication.
That said, Stumbling Feint specifies:
When you use Flurry of Blows, you can attempt a check to Feint as a free action just before the first Strike.
And gives some additional benefits as part of that feint to both attacks from Flurry of Blows.
How can Luce ever benefit from this archetype feat, unless Luce also multiclasses Monk to get access to Flurry of Blows? Is this just an oversight from Paizo?