Excel 2013 Document-Level Add-In Not Working in Excel for Office 365

I've written an Excel 2013 add-in in C#. There are also some VB macros embedded in the specific Excel spreadsheet (from which the VS project was created) for interfacing with the C# project.

I also created an installer for the add-in using https://docs.microsoft.com/en-us/previous-versions/visualstudio/visual-studio-2010/ff937654(v=msdn.10).

Once I run the installer, I can open the spreadsheet (an XLSM file) in Excel 2013 and run one of my macros, which in turn calls some C# code. This works fine.

When I open the XLSM file in Excel for Office 365 I get a VB error saying it can't find the project/library. If I go into the Visual Basic editor > Tools > References, I can see that there is a MISSING reference and the path given is DESTINATION_DIRECTORY\{C804DD24-544E-4DC8-A4C6-02F8B961D50A}. This last part seems like an Interops component ID but I'm not sure for what.

Any help would be GREATLY appreciated.