If your Plumeria seeds do not germinate, there are several factors to consider. Check the seed quality and viability, as old or non-viable seeds may not germinate. Ensure the seeds were sown in a suitable and well-draining seed-starting mix and kept consistently moist. Check the temperature and lighting conditions to see if they meet the requirements for germination. Some seeds may require a longer germination period, so patience is essential. If necessary, you can re-sow the seeds, making sure to adjust any environmental factors that may have affected germination. Experiment with different methods to improve germination success and consider growing more seeds to increase the chances of successful germination.