cashu.me is easiest because you don't have to ask any questions. It's the lowest friction solution usually but it's not uncommon to have issues with the camera permissions. This happened yesterday with the uber driver.
I have also had issues with iphone lockdown mode failing to render the correct fonts. It's not a dealbreaker but it looks ugly and is not the best first impression to make.
Best is to switch to a thick client app in this case. For android I recommend minibits, macadamia on iPhone. But the best wallet keeps changing. eNuts is making a comeback for iPhone. Minibits also just launched on iPhone iirc.
I'm not an iphone user so I just crowdsource app recommendations. YMMV