Authorisations are used commonly for internet payments to ensure that a card is valid. You might have noticed that if you sign up for a subscription online, request an Uber, order a pizza, or any other transaction that you provide your card for, the merchant will usually place a transaction for a small amount on your card, usually about $1. This is exactly the same thing, and this amount will disappear any time from a day to a month after it is created.
If the merchant were not to do this, anybody could provide any sequence of numbers as a credit card and the merchant would have no idea whether they will be able to receive payment after they provide the service. We request an authorisation on your card for the amount of the service for the same reasons. We place an authorisation the day before the service so that if there are any issues, we can get in contact with you before your service time so that we can sort out any problems with the card.