You are right - should be "these" as "ліки" in Ukrainian are plural. But still - "this" is better here than "it"
"Це не є моє лікарство!" grammatically is: "This is not my medicine!" (It is singular. 'Ліки' is definitely plural.)
"Лікарство" is definitely not a thing in Ukrainian. And "ліки" is uncountable
"This is not my medication" is not accepted. Is that because there is a different word for medication?
In English, "medicine" is used for singular and plural. My guess is because you could have 1 pill in a bottle, 100 pills in a bottle, a tube of medicated lotion, or a bottle of cough syrup meant for however many doses -- it's all still "medicine". We don't use the word "medicines". However, we do use "medication" and "medications".
For example, a paramedic could ask: "Are you taking medication?" (Answer: "Yes.") Response: "What medications are you taking?" - to imply the user might have more than one type of medication for different things.
This is why I think the words "medication" and "medications" should be allowed in these exercises.
Thanks for considering!