Hi SalesManager could you perhaps send a screenshot to show the form you are using for your appointments, to show which fields you are using to define the required and/or optional attendees. Out of the box the standard form and functionality does allow you to invite many contacts, accounts etc to an appointment as shown below, but there is a chance perhaps that you are not using the out of the box fields and may have some custom lookups in use? Please update with screenshots and/or check that you’re using the standard ‘required’ and ‘optional’ fields as shown. in this example I have just selected one contact, but you can see the ‘add more records’ capability and this includes selection of account records.