@woozle I was able to update it offline as you suggested. I wasn't sure if I should since the router was purchased in India and the India support page for C80 didn't have that firmware version...

I'm running firmware 1.13.2 Build 230824 Rel.74702n(5553) on Archer C80 (hardware revision 1.0) and I can see that version 1.13.15 Build 240812 Rel.53634n(5553) is available on the firmware updates...