If you click on the little “i” next to the promo you’ll see that the $65 plan promo is available to new and existing customers but that the $60 one is only available to new customers.

Thank you Allan. That helps explain it. I thought I was going mad.

I specifically called and spoke with someone about this, and the lady on the phone told me that both plans were available to me when I upgraded to an iPhone 13 (I am an existing customer). I asked her why I could see the $15 credit show if I chose the $65 plan and got to the checkout, but the credit didn’t show when I chose the $60 plan. She told me that it just doesn’t show at checkout, which I thought was odd why it would show for one plan but not the other. Turns out she gave me false information by telling me that I qualified for the $60 plan, that I ended up purchasing, and now I have to wait 2 days for a callback to speak with someone to get this sorted out. Not thrilled, and hoping they honor their employees mistake...