Whether paying someone back has a positive connotation or a negative one will depend on context. So if someone wronged you and you said you wanted to pay that person back, it would have a negative connotation because it would mean you want to wrong that person. However, if someone did you a favor and did something good for you, paying that person back would have a positive connotation. To give you more variety in how you can express this idea, I wanted to give you some extra options for how you can say, “I’ll pay you back for the favor you did.” “I want to return the favor.” “I owe you one.” (This is a common expression.) “I feel indebted and wanted to give back what I owe.” “I want to express my gratitude by giving to you what you gave to me.” “You did something good for me. I want to do something good for you too.” “I want to give to you as you gave to me.” “I want to express my gratitude by helping you as you helped me.”

In comparison to notebook entries, discussions seem to place a much more heavy restriction on the amount I can write. (This text box kept stopping me and the text format kept changing.). I had a much more extensive reply prepared for you with more sentence suggestions. But, I had to settle for what italki would allow me to write. That is, assuming you wanted sentence corrections. Aside from saying that, I would love to dialogue with you and hear about all your lovely adventures. :)