The smart move is to buy and install your eSIM at home, days before you fly. You need wifi to install it, and you will have plenty of that at home. Once it is installed, it just sits on your phone and waits. It does not start using data or counting down its days until you arrive in Samoa and switch it on.
First check that your phone supports eSIM. Most phones from the last few years do, including recent iPhones, Google Pixels, and Samsung Galaxy models. Your phone must also be carrier unlocked. After you buy a MegaEsim plan you get a QR code. On an iPhone go to Settings, then Mobile Data, then Add eSIM, and scan it. On Android look under Network and Internet, then SIMs. That is the whole install.