If you're using Privacy on Contacts and your team can't see all the Service Providers

Behind the scenes, Appointiv uses Contact records to represent Service Providers for bookings even if the Service Provider is a Salesforce User.  So, for that reason, if you are making Contacts Private, you may need to create a way to share the Service Provider Contacts with everyone. 

To do this, create a new Account - call it Appointiv Service Providers for simplicity.

Find all the Contacts that represent your Service Providers and add them to this Account.  (search for the field "type of record" = "service provider" to find them easily)

Create a sharing group.  Call it Appointiv Service Providers...or something equally obvious.

Add all your users to the Sharing Group.

That should solve the issue.