It is true that in most cases a singular count noun must be preceded by a determiner such as a, the, this, my, every, etc. The problem is that many nouns have both countable and uncountable uses. If the use is uncountable, then a determiner is not always needed.
License is one such noun that can be both countable and uncountable. If you are referring to some documentation that permits you to do something, then it is countable and needs an article:
I have a license for my dog and a license to fish.
However, license also has the more general sense of permission to do as you please, in which case it is uncountable:
There is a distinction between freedom and license.
In your sentence license seems to have the first meaning, so I would put the indefinite article a in front of it.