TDS defaults trigger late fees, interest and penalty under GST, with refund limits where credit is already applied. Failing to furnish FORM GSTR-7 or the TDS certificate within prescribed periods attracts per day late fees under CGST and SGST/UTGST subject to caps; failure to deposit deducted tax attracts interest from the due date and determination of default follows assessment provisions. Defaults in deduction or payment expose the deductor to a penalty equal to the amount in default or a prescribed minimum. Excess or erroneous deductions follow refund procedure, with no refund to a deductor if the amount is credited to the deductee's electronic cash ledger. Rejected TDS credits must be amended and resubmitted for supplier action.