Jan. 12, 2021 4:55 pm ET After a week of unsuccessful attempts to book an appointment for a Covid-19 vaccine, Katie Solovey’s parents turned to her for help. The 34-year-old’s parents spend their winters in Siesta Key, Fla., part of Sarasota County, which is using Eventbrite Inc.’s ticketing platform to schedule vaccine appointments. The platform is familiar to Ms. Solovey, but not to some older people including her parents, who are in their 70s, she said. Her father was also using a first-generation iPad on a shaky wireless connection, making it hard to ente...