I need some changes to an existing website

I need some changes to an existing website. Hello this is my 3rd attempt to finish and make possible one website that has been previously developed by some freelancers here without any success. They didn't finish and couldn't complete the job due to API configuration problems. My goal is to have a better website than [login to view URL] which sales unlock services solutions for almost any mobile device. This is a website that sales mobile unlocking services only, there is not tangible items here, only services. The big challenge here is the back-end development. It needs to be API compatible with similar websites to receive unlock codes or IMEI numbers. I attach API documentation which can be also be found for free by searching in google, but you will need to do all the configuration. If there is any extra cost involved in API development, or sandbox or anything else, it will by covered by freelancer itself; Any other extra cost involved in the project development or design will be covered by freelancer. This is not a simple project as I mentioned previously, some freelancers already tried to develop it without success and they received negative feedback from me and their freelancer's accounts are now limited. So please don't come to me if you're not sure about this project. I have waste to much time and money to make this happens without receiving the desired results. This is NOT an e-commerce website; all back-end development needs to be done from scratch and make it compatible to sale mobile unlocking services as unlockbase.com. The website itself doesn't make the unlock process and doesn't unlock any phone, it only receives information (IMEI code of the locked cellphone) from other websites or customers or any person and that info is forwarded to source via API or manually, when the order is ready, there are two way I can receive info: 1. Automatically: the unlock code or confirmation messages are received in my website automatically if I have API connected my website to source's website, 2. Manually: I get notified about the order completion message via email or something and I manually forward order info to my clients or to other websites . API is mainly for communication automation between websites and the unlock process is made manually by source or by me, but the website will not do the unlock process.