Add the buy/sell logic for my current wallet project. -- 2

I have the cryptocurrency wallet project what has BTC/ETH/.. options. Current the most of payment method is done. ONly needs to implement the buy/sell logic. I want to implement the buy/sell logic with the 3rd party libraries to reduce the time and budget. Please apply if you have a really experience and Please share your project url what It have buy/sell function. If not, I will skip that. That's the long-term project and Needs to find the right person.