mgeo I am not really sure what do you mean tax ID, because for my country it is the same as personal identification number. But european financial instutions are required by law to give information to tax authorities. Based on that i would assume that if tax id is required to do that in your country, it would need to be given to icard.
I first tried to use icard without any google services, downloaded from aurora store, but it did not work. In my current setup download it from google play, but i dont't know if that is requirement, but at least play services are needed.