You're going for a diploma even though you have a Master's degree and work experience of 3 years. It might get a tad difficult to convince the visa officer considering you already have in your possession a much higher level of qualification. Nonetheless, you could write a very intricate letter of explanation, pointing out the very important reasons for choosing this diploma program even after having a rather high level of education. You should mention how this program is going to level up your career and why you are pursuing it now. Just be honest and smart in explaining your career goals and plans. Don't be vague, be clear and concise and you might get your visa after all. Good luck!
