Does the Calendar Work in Instant Web Publishing?
No. Instant Web Publishing (IWP) is the older version of what's now FileMaker WebDirect. None of SeedCode products come with IWP layouts.
What About WebDirect?
Yes. While DayBack for FileMaker (the one you embed in your files) doesn't work in WebDirect, DayBack Online does. You can point this at the same tables as DayBack for FileMaker and use it in WebDirect or in plain old browsers.
Learn more here: https://www.seedcode.com/filemaker-webdirect-calendar/
Need to Use the Calendar in a Browser?
Yep: DayBack Online works in browsers as well.