"...may not see the value of our platform yet or that they already have an existing older system."

This is where you want to focus your energies.

Why don't they see the value of what you're offering? What roadblocks exist here and how can you remove them? Have you spoken with existing clients to see how they are using your service and what they feel is missing? What was their feedback and have you implemented it into your system? What is it about their old system that they feel is better than yours / or that yours fails to overcome a certain shortcoming and is not worth the hassle of migration?

I think some digging into your clients is in order. A better picture needs to be painted about their needs and how they perceive that value that you offer.