Hi Mike - Kind of sorted it. The syntax is a bit fiddly but here is one example with a filter and a sort:
http://<UID>:<PWD>@<TVH-IP?:9981/api/channeltag/grid?filter=[{"field":"index","type":"numeric","value":"100","comparison": "LT"}]&start=2&limit=5&sort=index&dir=desc
The issue was that the API does not show items from the GUI that are not ENABLED. Not sure if there is any way of changing this. Once an item is disabled, then the API will not show it. So if I disable something I will not be able to re-enable it!