To add salt to injury

This mixup was found in the following newspaper:
https://www.channelnewsasia.com/news/singapore/commentary-what-can-a-chief-commuter-engagement-officer-do-to-9928296

It is a congruent conflation of  “to rub salt in the wound’ and “to add insult to injury”, both meaning to deliberately make someone’s misfortune or unhappiness worse.  “Wound” and “injury” are similar meaning words, probably creating the mental mashup.  Now if the writer had written “add-in salt to injury” that would be an eggcorn.  An eggcorn is a similar sounding phrase spelled differently.   Because of the similar sounding words, this is a very common malaphor, with over 2,300,000 hits, according to Google.  A big thanks to Eve for spotting this one.