KYB Solution Recommendation ( I will not promote )

Hello everyone, I am working on a SaaS product targeted towards Merchants in the US and I am trying to find a KYB solution that could help me onboard Merchants seamlessly. I have been to trying to get access to the solution from Persona but its been just too difficult to keep waiting on their slow responses. Does anyone have experience working with a KYB solution that supports Hosted Flow so can be onboarded quickly and have a sandbox environment before I need to pay for the solution. Please guide!