The user has the Salesforce Community Plus license and all permissions set, but still, we can see the error "User does not have the required permissions on the Work Order object". The user has access to the work order object.
The user profile should have access to the Entitlement field on the Work Order and to the Entitlements object.
After adding the required permission for the field and object, we can see the book appointment is working correctly as shown below.
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