I’m seeing lots of <<function missing>> references in some scripts and calculation fields – is my fmEcommerce Link file broken?

No – if you’re using FileMaker Pro v16 or later it won’t install the FileMaker plugin which is required by FileMaker Pro v15 or earlier. Those fields/scripts with the <<function missing>> references are the ones used by the plugin. In FileMaker Pro v16 or later we were able to replace the plugin functions with native FileMaker script steps and functions, so these  <<function missing>> are the references to where the plugin functions would normally appear (if you install the BaseElements plugin these will appear again). You can just ignore these if you’re using FileMaker Pro v16 or later as they are not required or used with v16 or later.