@Alice *******
Yes, exactly. You need to have:
1. A valid Vietnam visa/entry stamp
2. Your actual address in Ho Chi Minh City (hotel or apartment)
3. Be physically present in the consulate's jurisdiction area (for HCMC consulate it's Southern Vietnam)
I used my apartment address in HCMC, but a hotel address works too - just make sure you're actually staying there during the application process.