Do I need to prime between the base coat and the top coat

We have applied the base coat EWI-225 premium base coat in 2 stages with the mesh in between we are going to apply EWI silicon render-075 as the top coat; do we need to apply a primer? I spoke to EWI and they said it’s optional!? No real explanation

So I wondered what you guys think, do I need to prime and if so why and why might it be optional?

Cheers