Hello everyone, long time no see!
USPS Informed Delivery revealed a letter from USCIS that was out for delivery yesterday. Unfortunately, it still has not arrived. We assumed it was the biometrics notice, so we contacted the USCIS live chat agent to confirm the date. It's a good thing we did because the appointment is scheduled for next week! We still do not have the letter in hand, which is required for the appointment, but the agent recommends reaching out again on Thursday morning for them to put in an emergency request to receive an electronic copy. I will update you all soon!
PS, do not delay contacting USCIS if a letter does not arrive after appearing on Informed Delivery. The appointment was scheduled for only 10 days after the postmark!!!