Recently I have been receiving private messages from two former colleagues whom I worked closely with while was working as an intern at my previous workplace. The first guy was my supervisor, he wanted me to work on a project I was solely working on as an intern (now the project needs to go on the market but it had one issue of missing component), I initially accepted the request to work on it because I felt I didn't leave enough documentation on most of the components. After the first fix, I got another issue fix request but I turned it down and since then he don't connect with me on WhatsApp like before. ( I'm a bit worried but I think what I did what's right ).
Just today, I was contacted again by another colleague, this time he needs help on a project they are about work on. When I was there, normally on my leisure time, I research on how to build applications on the company's APIs and one idea that came up was Invoicing. I started working on the idea and even started coding from the company assigned laptop ( It wasn't a crime as an intern and as long as the company didn't have such project, I was okay to work on it). I did asked questions on how the existing system works and this colleague was always explaining things and at that time I had no intentions to leave the company so I was planning to discuss the idea with the CTO and unfortunately I couldn't have the chance before my internship ended and I left the company. Now this friend said he need help on how I was implementing the invoicing idea as they have a new CTO and they want to implement something like that, but I want to turn his request down because after my research I realize that the idea was bright and I have been working on it ( implementation and connecting with potential investors (local banks)).
I don't know if I'm doing is right or wrong regarding my relationship with them personally and legally is it okay continue with the implementation as my own product?