How do I show HSN and SAC codes correctly on my repair invoice?

Tag each parts line with its HSN code and each labour/service line with SAC 9987 (or the correct sub-code) so your invoice matches what you report in your GSTR-1 HSN summary. Repair-shop billing software like BytePhase lets you set the code once per inventory item and job-sheet line, so every estimate and invoice generated from a repair ticket carries the right code automatically instead of relying on someone retyping it correctly every time.