I think it means like "I/you did this for you/me so this..." but the phrase is not complete so it's hard to understand. Example. 네가 도와해주나깐 이걸 좀 받아. = "You helped me, so please take(recieve) this."

해주니깐 = 해주니까는 --> 해주니까+는 이걸 = 이것을 지금 바쁘니까 나중에 전화할게 --> I am busy now, so I'll call later. To explain your phrase 해주니깐 이걸, why don't you give some situation or context?