Letter of Undertaking replaces bond for export without integrated tax, subject to eligibility, execution and payment conditions. Allows registered persons to furnish a Letter of Undertaking in place of a bond for export without payment of integrated tax, excluding those prosecuted for significant tax evasion; requires the Letter of Undertaking to be submitted in duplicate on letterhead in the annexure to FORM GST RFD-11 and executed by specified authorised persons; non-payment of tax and interest within the prescribed period leads to withdrawal of the facility and restoration only upon payment; applies mutatis mutandis to zero-rated supplies involving SEZ developers or units.