I pick up my STPC vouchers either at SFO or CCU, my origin/dest airports, for my Dubai stopovers.

From the US, I always book the STPC stay on the customer service number, which usually connects to Mumbai it seems.

In any case, the agent can book your stay, and also email you a copy of the reservation. You can then use this to pick up your STPC voucher at SFO airport.

I have done this nearly 20x with no issues so far (fingers crossed).

I hope this helps.