Udyam is the current MSME registration. It classifies a business as micro, small or medium using investment and turnover, and it is filed against Aadhaar. The government portal does not charge a fee.
The certificate does not give you a licence to trade, a GSTIN, or a loan by itself. Banks, GeM and some tender documents ask for it as a classification proof. Payment-protection rules for micro and small enterprises also look at this status, so a real supplier should not ignore it.
Figures are increasingly pulled from income-tax and GST data. If you type a turnover that fights your GST returns, expect the classification to be corrected later. File it after PAN is live, and after GST if you already have GST.
Digital Filings charges a professional fee, starting from INR 499/-, only when you want the application prepared and checked. You can always file it yourself on udyamregistration.gov.in.