# Incorporating Fixed Effects with Causal Impact

I have observations on a dependent variable of interest, $$Y_{ijt}$$, where $$t \in [1,2,...T]$$ denotes the time, $$i$$ denotes a particular brand and $$j$$ a specific product item. At $$t=k$$, there was an intervention, corresponding to the opening of a marketing channel used by some of the brands $$i$$ for some of the product item $$j$$. I want to use Causal Impact analysis to look at the effect of the marketing channel on the variable $$Y$$.

If I were to use traditional difference-in-difference analysis to look at the effect, I can incorporate fixed effects corresponding to the brand $$i$$ and product $$j$$. How can I incorporate these fixed effects in causal impact analysis?