That is unusual that you got both invoices at the same time. Everybody else just got the NVC Welcome letter with instructions to go online to start the process by first paying the AOS Fee and then completing the DS-261. After the DS-261 is completed and approved they send you the IV Fee Invoice, which is where we're all stuck on and why we're here.
I got my notification that my DS-261 (agent assign) was approved with my IV Fee Invoice on June 16th, and to this day It's not letting me pay it online, therefore not letting me access the DS-260 online.
It looks like most people are waiting 3-4 weeks after they receive the IV Invoice before it lets you pay online. I'm a little over 10 days and waiting.
Just a thought, maybe since you're using a lawyer it's a little different. I'm not sure as I'm doing this myself.
The lack of transparency throughout this total breakdown of the NVC's website has been demoralizing. At least the people who had trouble receiving their printed visas these past few weeks have gotten daily updates on the system fixes and worldwide media coverage of the problem. Everyone here looking to fill in their DS-260 or pay their immigrant visa fee on the other hand has been kept in the dark for weeks if not months. When is anybody from the NVC going to level with us about what's going on? Why is there no coverage of this? If it weren't for the fellow commenters here helping to crowdsource info together I'd be going even crazier with doubt and worry.