Thanks for the response. I contacted Evolve directly as you advised. They responded "Yotta Savings is not a direct Evolve customer. They are linked to our bank through our financial partner, Synapse. You will have to contact Synapse so they can better assist you."
So I'm unable to get confirmation from the FDIC-insured bank that you're using that their FDIC insurance extends to your customers. Sure, I can contact Synapse, but I don't know why I should trust what they say any more than what Yotta says - Synapse isn't FDIC-insured either.
While looking for this, I also found a medium post by Beam (https://blog.meetbeam.com/a-primer-on-fdic-insurance-72fe688...) who explain how their savings accounts are FDIC-insured upto $250,000 for every customer - they would open an account in every user's name at Evolve bank. Perhaps it would help you gain more trust if you did a similar post.