Some pumps offer a "Fill Up" option. It will then state that it will hit yor card for xxx gallons or $zzz dollars, normally around 100 gallons and $600. That will hit as a "pending" charge until the actual amount of the sale is posted and verified. Sometimes that can take a day to clear.
If the pending charge will exceed any limits on your card the card will be rejected and the system will not turn on the pump.
It is recommended to select gallons and a quantity, the pending charge will be for that $ amount. If you pump less, the final sale will reflect what was actually pumped and the pending charge will clear and go away.