Whether any penalty if supplier not mention GSTIN in bill

If a supplier issues an invoice with GST applied but omits their GSTIN, you generally won't face penalties. However, this omission means you cannot claim Input Tax Credit (ITC) for that invoice. While the seller might still declare it in their GST return, and it may appear in your GSTR 2A, the invoicing rules state ITC is unavailable without the GSTIN on the tax invoice. It's advisable to obtain an invoice that correctly includes the supplier's GST number to ensure ITC eligibility.