I don't know if they are particular about it, but mine simply showed transactions across 3 months + final balance. It's a portal from my company where they send me payments, so they asked for business registration (I just sent LLC public info in the state where it's registered cos HR can't be bothered to look at articles of incorporation. Won't make diff either since my name isn't there). Basically in my case, they just want to know numbers make sense, and company isn't bogus (it isn't, business for 15 years now, been with them for 10 years)
Supply those certifications from various engagements. If through Upwork, you can download certificate of work through the platform. Or, ask 2-3 of your clients to create (or you can create for them) and have them sign, some cert you work with them, how long, how much etc or simply, invoices.
They might ask you for business registration or stickers of incorporation, so I would recommend you include it, to prove you have access to those funds.