Spotify issue plastic gift cards that can be bought in local shops. They are valid 12 months from purchase, and can be used to pay for spotify premium. There is no online balance checker.
Some websites also sell eCodes which we occaisonally sell, and these are delivered by email.
The Card is redeemable for full price standalone Premium subscription months only and cannot be redeemed for discounted or group subscriptions (such as student discounts, trial offers, Premium for families, or offers combining Premium with other companies’ products or services).