If you want to schedule Skype for Business meeting, it needs an exchange calendar which generated after the integration between Skype for Business server and Exchange server.
So, in your scenario, you cannot schedule Skype for Business meeting, but to use Meet Now feature to start an instant Skype for Business meeting.
Besides, I find a web-based program - Skype for Business Web Scheduler, which can create new meetings, change your existing meetings, and send invitations with your email .
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