"There is less sugar in my tea."
Translation:मेरी चाय में कम चीनी है।
This should be accepted. However, there is a subtle difference.
मेरी चाय में कम चीनी है is saying that there is less sugar in your tea but this is simply a statement of fact. Perhaps that is what you asked for. It is used, for instance, where you are asking someone to be careful not to switch cups while serving because one has less sugar.
In मेरी चाय में चीनी कम है, you are placing emphasis on there being less sugar. It would be interpreted as asking for more sugar.