The $1 transaction you may have noticed is called a “pre-authorisation”. When you sign up for Medipass or register a new payment card, a $1 pre-authorisation is made on your credit or debit card for fraud prevention purposes and to ensure your card is valid. We void that authorisation immediately so you are never actually charged - no funds have been withdrawn from your account. If you’ve used other online services like Uber before, you may have noticed that they do they same thing.
Note that while a pre-authorisation entry may temporarily appear on your online card statement, typically just one to seven days, the value was not and will never actually be deducted from your account. Your bank will be able to confirm this for you if you have any concerns about the transaction status.