I generally see "sign up for" online, but I've noticed "sign up to" in a few places. Is that an acceptable alternative when talking about signing up for a service?
For example, PayPal says "It's free to sign up to PayPal." Is "PayPal" serving as a verb in that case?
The same for the title of the Airbnb sign up page: "log in/sign up to Airbnb".