Can't Find 14-Digit Control Number on IRS Identity Verification Notice to Access sa.www4.irs.gov Portal

I need help getting into the IRS Identity Verification portal (sa.www4.irs.gov). I got their verification notice in the mail, and I'm on the "Verify Your Return" page where it says "Did you receive an IRS return verification notice in the mail?" But I'm completely stuck because they keep asking for a "14-digit control number provided on your notice" and I've looked at every single page of my notice multiple times but can't find anything that looks like a control number. The site says I don't need to use spaces when entering it, but that doesn't help since I can't even find the number to begin with. I'm currently looking at the exact IRS Identity Verification screen at sa.www4.irs.gov which displays "An official website of the United States Government" with the "Here's how you know" text next to it. I'm on the "Verify Your Return" page under the "Verify Your Notice" section. The screen specifically asks "Did you receive an IRS return verification notice in the mail?" and there's additional text that says "(You will need this notice to continue with this online service. If you received a notice, but don't have it with you, please come back later.)" I selected "Yes" and now it's asking me to "Enter the 14-digit control number provided on your notice, you don't need to use spaces." That's exactly where I'm stuck because I've scoured every inch of my notice and can't find anything resembling a 14-digit number. I see there's an option that says "No, please resend the notice" but it warns that "(If you have filed your return within the last 7 days, please allow an additional 14 days to receive the notice in the mail before requesting another one to be sent. You can then come back and continue verifying.)" I'd rather not wait another 2 weeks for a new notice if I can avoid it. There's a blue "CONTINUE" button at the bottom of the screen, but I can't proceed without this control number. Has anyone else dealt with this? Where exactly on the notice is this control number supposed to be? I feel like I'm going crazy looking at every single line of this notice.