First of all, this is a cash only restaurant where even debt card is not allowed. If you don't have cash with you, sorry! But you will need to pay a surge to use the ATM machine in the store. That will add an extra two or three dollar to your 8-10 dollar pho meal. ( not worth it).
Secondly, the host behind the counter does not has a hospitality attitude.
I don't know the exact reason why they are following that cash only payment practice, but that did made my experience with the restaurant unenjoyable.
There's other places similar in the city for more reasonable payment options. Will go for the alternatives for sure.