Some vendors, like hotels and gas stations, can hold funds when you swipe your card because they do not know the final amount of the sale (that is, the amount of gas that you actually pump). At gas stations, they usually release the hold within two (2) hours, but at most can be held 7-10 business days. You can avoid this situation in the future by paying for your gas inside at the register. Merchants like rental car companies and hotels can issue holds for up to 30 days.
You can message your Concierge in app for more details on specific transaction holds.