Office 365 is the paid subscription service offered by Microsoft. It doesn't matter if you load your appointments using the Online Outlook version or the Desktop version. If you have a Office 365 subscription you will be able to connect your Outlook Calendar to Appointment Reminder.
You might want to make sure sending is turned off before you connect your calendar so you can check what appointments are syncing before sending out reminders.
Login to Appointment Reminder. Go to Settings > Add Calendar > Office 365.
You will be asked to authenticate with Office 365
Once connected you will be given a list of calendars you have direct access to. If the calendar you want is not added listed click "Add Shared Calendar Not Listed" and enter the email address of the shared calendar you want to connect.
Click connect. You will need to repeat this process for each calendar you want to connect to Appointment Reminder.
You can then go to Calendar > Open Calendar to check which appointments have synced. This might take a few minutes. You will be emailed when the first sync is complete.
You can use "Keyword Mapping" if you want to send different scripts based on "Keywords"
You can "Negative Keywords" if you want to stop specific appointments from sending.
You can go to Settings > Edit Calendars > Edit and check the calendar settings for any calendar. There are a lot of settings that can be adjusted to suit your specific use case.
Remember to turn sending back on if you want reminders to start sending.