To use the StraboSpot/ArcMap Add-In for ArcGIS for Desktop v10.3.1 download the .esriAddin file found at: StraboOnline_Arc_7-28/bin/Release. Make sure to save this file to a known location on your computer.
To install: navigate to the esriAddIn file and double click to launch the dialog which will add the StraboSpot toolbar ('Download' and 'Upload' buttons) to your ArcMap 10.3.1 interface.
The Add-In toolbar could also be added by navigating to the Add-In Manager in ArcMap (on the Customize dropdown menu).
Please note that this version of the Add-In might not work in newer versions (e.g. 10.4-10.6) and will not work at all with older versions (e.g. 10.0-10.2). Newer versions will be released soon for 10.6.
Any issues or bugs can be reported to this GitHub- we appreciate your feedback!