Billing
What a membership changes
A paid membership changes four things:
Campaign slots — how many campaigns you can run at once.
Priority slots — how many campaigns can be prioritised, which does affect delivery speed.
Prices — what a campaign costs you.
Earning rates — what you are credited for the work you do.
Upgrading takes effect immediately and is charged pro rata. Downgrading takes effect when the period you have paid for runs out, so you keep what you bought.
Slots can also be bought on their own without a membership, and a subscription can be cancelled whenever you like.