Dear aspirant

You have not mentioned the name of the state entrance or the name of the counselling yet . For every entrance ( it can be either state level or national level) it must be mentioned that ews certificate approved by which authority is valuable and applicable for the counselling and admission processes. One must abide by those rule.  For all entrances the authority will not be same. However for one entrance both state and national authority is generally same.

So you must check whether the authority or post post that signed your state EWS certificate is applicable to sign EWS certificate in JOSAA counselling or not.

Best wishes.