This app requires a local phone number to receive the OTP to log in. So, useless for most tourists. Fortunately, the PCR test at the airport comes with a QR code so you can show your negative result without needing the app. 1* because this issue would be easy to rectify by using email verification or clearly stating a local # is needed. Some places also require Vax proof and they accepted paper US Vax cards and photo of Vax card. I imagine the app is fine if you have a local number.