Improper Watering Or Drainage

This looks like an issue caused by improper watering practices and/or lack of drainage appropriate to this plant. Improper watering (either not enough or too much), in this case it appears to be too much, can cause the leaf damage we see in your photo. If the pot does not have drainage holes, we recommend you move the plant to a pot that does have them. Water only as needed to keep the soil evenly moist, do not fluctuate between extreme dryness and flooding that removes all the air from the soil. And be sure that the pot and plant are not sitting in water in a saucer. Placing pebbles in the saucer to lift the pot can really help. Plant roots need a balance of water and air in the soil pores for healthy growth and development.