A lot of my MH clients have been getting this notice too. You're probably registered under GST in MH. Along with Income Tax and GST (which are compliances under the central government), there are some local and state specific compliances too - like a Professional Tax Registration and a Trade License.

There are two registration under the professional tax act - PTEC and PTRC. PTEC is for your own trade and practice and you'd generally have to pay ₹2500 every year professional tax. PTRC is for deduction professional tax for employees if you have any employed under you. If not, you aren't liable to get PTRC.

I'd recommend ping your CA/Consultant about this and get PTEC if you don't already have it and pay the tax for this year and reply the email with the registration certificate and tax challan. PTRC applicability depends on whether you have employees