Battlepass
Delve offers a unique battle pass which offers outstanding rewards over time just by playing the game. You unlock tiers by getting XP which can be through skilling, bossing, training, etc.
There is a free and a premium pass. You will automatically begin accumulating progress from the start of your account and will unlock rewards for both pass versions. However, you will need to purchase the premium pass from the store for $30.
The rewards that can be achieved are excellent and purchasing the pass is probably the smartest/most efficient way to donate in Delve. You can use ::bp in-game to view rewards for levels 56 in total. Pass resets every 90 days.
Buying the pass does NOT add to your total in-game donated only consuming scrolls will progress your donator rank. But you will receive scrolls in your premium pass rewards. (edited)