It isn't.
I assume you're in a 30-day trial period. Once that ends Prime will turn into Prime express which disables:
- Symbolics,
- Programming (but you still can define functions, even fairly complex functions).
- Solve blocks.
- The chart component (but that's really not a miss).
- ComboBoxes.
- Premium features (such as Re, Im, mean, stdev and many many more)
Many of the Premium functions can be built from functionality that is still supported, if you're interested: https://community.ptc.com/t5/Mathcad/Prime-Express-A-joke/m-p/604216#M185378
If you really do need the symbolics, you'll have to subscribe to a license.
Success!
Luc
