Our business has lots of price promotions. Times series technique will not work for us, we need to use causal methods like regression

Promotions are business events and not independent variables. Strong correlations with independent variables do require usage of causal methods. However, we need to firstly test the strong existence of this correlation and secondly using causal methods should give better forecast accuracy than time series for them to be deployed. Business events like promotions and stock outs are generally smoothened by marking an event in the historical data by a good forecasting software. It must be noted that causal methods are mostly less reliable than time series methods.