I resolved my OTP code issue, here: Definitive guide to time setting & sync in Qubes OS - #15 by tanky0u
To summarize: my system clock seems to have drifted from the UTC clock. The mismatch was around a minute and a few seconds apart. The sys-net qube had its template on a minimal debian-11 template. I created that template following the qubes-os documentation here: Minimal templates | Qubes OS
The guide didn’t mention installing the debian package, systemd-timesyncd. And it wasn’t present in my sys-net minimal debian-11 template. So, as suggested by @rustybird on the afore-linked thread, I have installed systemd-timesyncd package to my minimal debian sys-net template using apt package manager.
I gave my QubesOS a restart, and now my clock is synced, and my OTP codes for this forum are working again.