Your problem isn't expertise. You know your expertise.
Your problem is likely pitching and packaging your expertise in a way that clients readily see the value in what you provide.
That was me.
I knew I had a high-level of expertise. I'm an award -winning attorney. I have studied business in Brazil, the Dominican Republic and Jordan!
I helped co-create a class in Morocco while at Northwestern Law. But even with all that... I was undercharging for my message and happy about getting what I could... now isn't that imposter syndrome personified?