This, unfortunately, can happen and is normal for gas stations. For some merchants like gas stations, car rentals, and hotels, a pre-authorization hold (usually around 15-20%) is placed on your card. This is by no means a charge, however, is standard to ensure you have enough to cover the purchase (plus incidentals where applicable). The correct amount will ‘settle’ within 10 business days after the purchase (7 business days for gas stations).
Tip: This happens on all credit cards, but more noticeable on KOHO because of our realtime transaction reporting. For gas stations, we recommend going into the station to request the dollar amount you want, or selecting a lower amount as the pre-authorization maximum at the pump ⛽