Hi Nataliia, saying "I will pay you back" doesn't always have a negative connotation. Only if you use it to mean "I will get revenge". But it's pretty common to say "Can I borrow $5? I will pay you back." If it's not money you are discussing, but an exchange of favors, then you can say "I'll return the favor" or "I'll make it up to you". Or even "I will owe you one", meaning, I will owe you a favor if you do this for me. So you could say "Can you baby sit for me? I will make it up to you". Or "Can you wash the dishes for me? I will return the favor". I hope that helps! ~ Helena ~

I would probably use "return the favor" in this case :) so for example: "Thank you so much, I will definitely return the favor" :)

You could just say "I owe you this".

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.”