Spearmint kinda Musky
When processing leaves into tea, there are three important steps:


Withering: this happens in the shadow or in the sun depending on what tea you want to make. In your case, I think sun-drying is proper. The goal is to allow the leaves to dry and soften a bit.
Rolling: after withering, you can roll the leaves, to squeesh the flavor from the inside to the surface.
Fixing: after rolling, you need to intensively dry the tea, for example in the oven. This is important to stop the oxidation process and reach a water content level below 5% (otherwise mould will develop later).


So if your tea tastes off, you have to check which step wasn't properly done. Since your tea was musky, it might be that the last step of fixing, wasn't done properly.