Took me an hour or so to figure it out late Friday night (this post was just approved, so sorry for the odd timing). While the "I'm Ready" button and the "Assistance Hub" only work with a separate business login (ie personal and business not linked), the signing documents are only available through the original account that the application was originally submitted with.
So for me, I signed up with the linked business and personal online account I've had for years. Then after nearly two weeks of waiting, Kiara a wonderful BofA rep, created a business only online account for me and voila, my application was complete, sent to the SBA and approved. Received the final documents (promissory and attestments), but could only access them through the original, linked online account, not through the business only account. Signed them, and received the note that I should receive funding within a couple of business days. Oh, and Safari didn't work for the final signing. Had to use Firefox.
What a process. Praying that it actually goes through. . . .
Good luck to all!