Unfortunately, this is quite far from a likely investment. Several big issues:

(1) It requires a great deal more work (read: "time+money") to SELL an app than to MAKE one. The primary risk investors need to overcome is not the question of whether the app can be built... it's whether the app can be SOLD. So if you haven't been able to demonstrate sales traction yet, then this is an unlikely investment.

(2) When an investor is in the same country, it's much easier to enforce the law. If someone in the US were, for instance, to transfer funds to a Ghanaian bank, and then you were to simply walk off with the money, they would have very little recourse. The idea of interacting with an overseas court system is a nearly unthinkable headache. I don't mean to offend or accuse you of bad intent — just pointing out that investors have enough fear within their own countries; it's compounded when looking at a foreign opportunity.

My advice is that you'll need to find a way to finish the Minimum Viable Product on your own steam, show some sales, and THEN pursue investors.

If the opportunity is so strong, for instance, perhaps you can convince your Serbian colleague to invest his own time in completing the project — in exchange for shares in the enterprise? If you hope to convince an investor to give you cash, then a good "baby step" would be to first convince a developer to give you their time...

Happy to discuss further on a call, if you like.