Replace acerill app

[AuBelEtage]

Shoppify has unilaterally decided to remove the acerill app from their range. We are a private wellness center and used acerill in combination with google calendar for all our appointments. Since an appointment can only be booked once, it is important that there is an interaction with the google calendar : on the one hand an appointment must be registered in the google calendar and on the other hand the system should not allow an appointment if the time is already taken. For now I can't find any app that provides that. Can anyone help me ?