Most likely, the sparse and crispy top of your String of Pearls is due to your plant not receiving enough light on the top of the pot. This is an easy fix! You can take a couple of strands of your Pearls and lay them on top of the soil. Use some garden pins to pin them down, so they are touching the soil. Within a few weeks, these will send new roots down into the soil, and your pot will appear full and beautiful again! Make sure that the entire pot is receiving enough light to prevent this from happening again. At least 4-6 hours of light per day is ideal.
The sparse top of your String of Pearls can also be caused over-watering. Make sure to only water your plant after the soil is completely dried out. Make sure to use your finger to check the soil. String of Pearls is a drought-resistant plant and is prone to over-watering and root rot. A sign that your plant is thirsty is when the pearls start wrinkling and look smaller. When this happens, you know it is time for a drink of water!