Have you tried this ?
#include "Curves/CurveFloat.h"
UCurveFloat* Curve = NewObject<UCurveFloat>(this);
Curve->FloatCurve.UpdateOrAddKey(0.f, 0.f);
Curve->FloatCurve.UpdateOrAddKey(1.f, 1.f);
TimelineRecoil.AddInterpFloat(Curve, ProgressInTimelineFunction);