Brazil Localization - ICMS Substitution Tax

Hello All!

We use a 3rd party flow where we send a PO to vendor in order to sell to our customers. We are now requested to use ICMS Substitution tax, law just published to be applied from June 1st. In the chain the vendor will pay for the ICMS, however we in order to enter invoice from vendor calculation with reduction base is not working, we are getting incorrect numbers. How should we calculate substitution value from reduction base?

Kind regards,

Fabiana