Hi Nick,
You would need to import the XY data into a Geodatabase and then add that new feature class to your map... before publishing to ArcGIS online.
Unfortunately didn't work. Should I convert the coordinate system of all the layers to WGS 1984 Web Mercator Auxillary Sphere or another co-ordinate system. I don't understand why I can create a visualise web map with all the layers but not a exploratory web map.