Dear Abdul Basit,
The employee has made a purchase from the "personal company" and submitted the sales invoice. However, who owned this "personal company"? Did he own the company or was it owned by the employee's spouse, brother, sister etc? What was the nature of the purchase and who approved this purchase?
A conflict of interest occurs when an individual’s personal interests – family, friendships, financial, or social factors – could compromise his or her judgment, decisions, or actions in the workplace. However, do you have a policy on conflict of interest? If yes, then has it been communicated and how has it been communicated? What if the employee feigns ignorance on anything like "conflict of interest"?
Creating a policy on conflict of interest is a time-taking process. This is a part of the HR consulting activity. It will be difficult to create a policy that suits your needs exactly.
Thanks,
Dinesh Divekar