There is a Robert Kunz who received an Invalid's penison, IC-3538 file #24669 for service as a Private in 4th US Inf. You can order the record for about $50 from the National Archives on line. An Invalid's pension is awarded to those who were injured or sick and could not work as an able-bodied man.

You could also request his bounty land record for about $25 which may or may not have any information about his infirmaties.