Documenting requirements
How you document the requirements coming out of these sessions is up to you, but write them down and make sure that all the members of your team have access to the requirement document(s).
Not everyone can join every call, but if you have one person helping the client with procure to pay and another consultant working on order to cash, they need to be able to compare notes and look for any overlapping concerns as they work things out.
You need to share these files with the client as well, of course. We commonly share files via the account's File Cabinet since this is a secure way to get information to all parties, and everyone has access to the account.
Next, decide on an approach that fits with your overall project methodology. If you're working with the waterfall method, you might decide to capture all the requirements in a single document (MS Word or Google Document, for instance).
You will want to keep revisions of that document as...