What's the best way to model tax credit?

[qzaus]

A positive tax works like an additional cost, and a positive subsidy like an additional revenue.  It is recommended to use positive values for both taxes and subsidies. So instead of defining a negative tax, it is better to define a positive subsidy.

There is basically nothing else needed to make taxes or subsidies correctly incorporated in a model, as long as the currency specified in the parameter(s) is correct (it should either be the only currency in the model, or a currency  converted to the target currency in the model). In VEDA, if you leave the currency unspecified, VEDA then assumes the default currency (as defined in SysSettings), which is usually also the target currency.

You should see at least the objective value being affected, if any of the processes having taxes/subsidies defined are active in the solution.

Thank you, Antti!