Holybro Kakute H7 + Hobbywing 50A ESC won't calibrate

Hello, I have built a PNP TBS Caipirinha 2 with a Holybro Kakute H7 FC and a Hobbywing 50A ESC (the one that came with it). I have wired the throttle to the motor one output and can see the PWM signal with my oscilloscope. After placing the plane in manual mode, I can see the pulse width change as expected with the RC throttle input. However, the ESC continues beeping and won’t do the initial PWM range calibration. I tried bringing the minimum and maximum pulse width to 1000 and 2000 uS respectively, but to no avail. Has anyone else had a similar experience?

Edit: The 50A UBEC does not support 6s. A 4s battery fixed this.

Max pulse (the noise is due to the ESC “beeping” the motor at that moment):

Min pulse: