auto-save 898.ctr

Game save attached to this thread. Issue also reported on Steam.

As Brazilians in the Contemporary Age, I can't construct missile units, both nuclear and conventional. I checked to ensure that I have sufficient resources and a silo district in the city where I attempted to build the unit. However, after construction finished, the units remain greyed out. The hover tip states "invalid spawn location." I built several more silos and skipped a few turns to see if the issue resolved, but it remained.

Looking at your save, in Harappa, following either one of these workarounds will unlock the silo :

1 - Moving a unit on Harappa's Main Plaza's tile :

2 - Building a unit on one of the spawn points (Main Plaza, garrison, or airfield) :

3 - Building a second silo, and then selecting the spawn point also unlocks missiles constructions :

That's a quite common issue, though in your case, it seems to be related with the activation of the spawn point for the silo, since garrison and airfield to the south of Harappa aren't concerned (working properly). Based on several related bug reports, this "spawn point activation" bug seems to have different causes.