Hot Events - Alchemy

[Androm3da]

event reqirements spend 10 diamonds reward 200k gold, spend 50 diamonds rewards 500k gold, etc.,

but I have spend 10 + 20 + 30 + 40 + 50 = 150 diamonds and only rewards 500k gold... Why can not I reward 1kk gold (spend 100 diamonds (50/100) rewards 1kk gold if you have already spend 150 diamonds ?

[BlackVerZ]

they state that you need to spend x amount at once. not total spend.