Looking for advice - how do you convince a customer to visit them onsite/at their office if they are hesitant? Any best practices that have worked for you?

Be transparent as to why that's the best thing to do and what the desired outcome is. They're being hesitant for a reason.

Do they feel like they're not supposed to have vendors come in office? Is there something culturally at their company where this would make it uncomfortable for them?

You need more understanding to what the resistance is before you pitch why it is a good thing for both you and them.

One best practice we employ is behavioral health digital nudging.

Nowadays we really want to save time and give time (=money) back to client. Being invited is more important and that happens when you can provide tremendous value.

The company I work for primarily functions in the warehouse and fulfillment space, and we face a multifaceted workload that involves balancing corporate and site visits. 

When we engage a customer and compel them to set an on-site visit, we focus on the tangible benefits and address their concerns directly (rational drowning). We highlight how an on-site visit enables a tailored solution, optimizing their specific workflow and ultimately saving time and costs. Then, if the resistance is there, we frame up their ownership around describing and capturing technical intricacies that we bring as an asset through the sales process. most people don't feel comfortable doing, and we get a visit time/date set.