I reuse the design guide "HB1Tone_Loadpull" and I have placed my PA (with the correct bias) instead of the transistor.
The simulation can't work if I fill : "S11_center" with 0 + j*0. So maybe I misunderstood the meaning of this variable. I thought it was the center of the circle of reflection coefficient that we want to simulate. So as I wanted to see reflections around 50 Ohms I have put 0+j*0.