California uses a destination-based, purchaser-address hierarchy for remote software/SaaS sales. SB 122 does not let you allocate by where the software is actually used. The order:
A subscription billed to a CA address is taxed; the same subscription billed out of state generally isn't. Clean, validated billing-address data is your biggest control — and your biggest compliance exposure if wrong. Collect and validate it at checkout.
Combined rate ≈ 7.25% state + district (commonly ~10.25–10.75%). Use the CDTFA rate finder for the exact per-address rate.