How often are you watering the tree? In hot weather you will need to water every week or so, but obviously a lot less in the dormant season [winter]
Liquidambars are deciduous... could be just losing leaves for early autumn... although it is summer over there I suppose.

new trees do need watering regularly but should not stand in water, I have trees that were planted about february and am watering them every couple of days as it is extremly warm here with warm winds but if its cold & grey less so but will still water regularly

Liquidambar styraciflua in native to wet, sometimes even swampy locations in the US, so it's highly unlikely that you are over-watering. Yours could be reacting to a change in the soil, since you have only recently planted it, or it might be objecting to a fertilizer or compost - they don't like alkaline conditions for instance, including chicken manure and lots of commercial potting composts. If it was in a shady location previously, and is now receiving lots more sunlight then it might be suffering from leaf-scorch (sunburn, effectively) Of course some varieties of L. styraciflua are actually golden-leafed too.