A number of people, myself included, have had trouble getting it to germinate. For 2 yrs I started mine in dirt and then rinse the roots, transplanted then prayed. Honestly I grow everything hydroponic except spinach now. Last year I cut off the bottom of an IBC, (the year before it was a kiddie pool) put rock at the bottom, covered with landscaping cloth and then put in a mixture of peat, compost, perlite, coco coir and some fertilizer. I added a float valve and attached it to a barrel of miracle grow to always keep and inch of water at the bottom... best spinach since I started hydroponics.
I had no trouble growing perpetual spinach.
Only problem was, I harvested first time as advised and they just shot to seed after that.
Trimmed the top 100mm off where the seed was then they went crazy rapidly shooting tons of seeds in all directions
We grow it in a deep water system. I put the seeds in water to soak for 24 hours before planting. It hen goes into the seedling dam until seedlings and then replant in large net cups fitted in polystyrene sheet. I just replaced a cropped that we have harvested from for 8 months.