Nauru eSIM
Your phone must support eSIM and be carrier-unlocked. Most recent phones support eSIM, for example iPhone XS / XR or newer, Google Pixel 3 or newer, Samsung Galaxy S20 or newer and most recent flagships, but not every model or country version does. To check, open Settings → Mobile / Cellular and look for an "Add eSIM" option. A phone bought from a carrier may be locked to that carrier.
Validity starts when the eSIM first connects to a network in Nauru. Prices include everything; your card is charged exactly the amount shown, in SGD.