Mentioning cin in agreement

Dear all,

We are enetering into Agreement with one of our cutomer and sanctioning him credit period. Now When I sent them draft for vetting purpose ,they revert with the comment that we need to mention Company CIN in the Agreement.

Now since commencement of the Companies Act 2013, we entered into many Agreement but did not mentioned CIN in the Agreement , whereas , invoices, bills ,letterheads contains CIN.

Now please let me know is it copulsory to mention CIN in any Agreement .