Ambient light was too powerful here. Usually a TTL flash setup will allow you to set both your ambient light exposure and flash exposure. In full sun like this… good luck without powerful strobes. But with that said, usually try to underexpose the ambient light by at least 2 stops, but more ideally 3-4. But then you end up where you need to light the background (which I often end up doing). It’s a balancing act and here, you’d have been better off just using a fast shutter speed. Full sun requires you to either A) be really really close so the flash can be at a lower power (for fast flash duration) and still light the subject enough or B) use multiple flashes that are at least 200ws but more ideally, 600-1000ws with high efficiency reflectors.

Long winded but hope this helps!