you need to make sure you are a verified user to use the card in foreign ATMs.
The card, although a prepaid card is just the same to use as a normal debit card - i.e. can use for contactless payments or insert into POS machine with your PIN number. - always chose pay in local currency for POS terminals and ATMs - some parts of Portugal don’t seem to want to use POS terminals and prefer cash for some reason 
The card can be ‘topped up’ instantaneously using the app with WIFI connection from your registered debit card that you used for your initial top up - so don’t ‘carry’ too much balance on your card at any one time just in case you lose it
Always useful to carry some cash with you - which can be withdrawn from ATMs once in Portugal if you’re brave enough to trust the card and carry no cash when you leave for Portugal - I usually carry about €100 on me when I go on holiday from previous hols - you will get a better rate in Portugal rather than exchanging in UK post office travel agents etc as its commission free and gets the mastercard rate of the day when you withdraw from a local ATM
Always carry another bank card with you just in case
you can find further information about Portugal by searching ‘Portugal’ using the frying pan top right of screen