Clients cannot add the appointments I send to their outlook calendar (incompatible error)

When I schedule meeting and sent the invite, clients are complaining that they cannot:

  1. respond/accept the meetings
  2. The meeting is not added to their outlook Calendar
  3. They claim my meeting message is “incompatible”
  4. They have to recreate the meeting, copy and paste the zoom code manually

I am new to EM Client and am wondering if I am doing something wrong or still need to set something up. It does not help if my meeting requests are not compatible with the corporate world using MS Outlook. Any assistance would be greatly appreciated.