Enabling the custom amount setting through ShineInsights will give your customer the option to place a custom amount of their choosing to the machine.
For example, if your dryer is set at $1.50 and you have the custom amount enabled, after scanning the machine, your customer will be prompted with the option to select the dry setting of $1.50 or enter a custom amount of their choosing in which case they could place an additional $.25 (or whatever amount they want) to the machine.
This feature would also come in handy if your customer would like to pay for part of their activation with cash and the rest with ShinePay.