U-Turn did not work on iPhone

While riding today, I tried to do a U-Turn, but the mobile app on my iPhone did not work. Is there something else I should do?

Did you hold it down long enough?It takes a few seconds,a graph fills up as before it turns you around.

@Sean

Thanks. I will give this a go as I had the same problem. I did see a little light blue line on the button when I pressed it but didn’t realise it had to fill the button before turning me around.