Introducing cheats doesn't work because the game has a leaderboard and I doubt cheats will bring more money. ----> However, you can have a look in your library, if I'm not mistaken there you will find a tool for the game, with which you can create your own modifications.

https://store.steampowered.com/app/451330/IS_Defense_Editor/

Otherwise:

Some of the upgrades are subtly worthless and hardly worth the points wasted on them. There are only 2 weapons, MG and rockets, the rest are modifiers and support from other troops, helicopters, artillery, bombers, infantry. Artillery and probably bombers also kill almost all of your infantry and too often you too.

If I remember correctly, if you choose the right upgrades, you have infinite ammo, except rockets. In the beginning you only have a limited magazine that you always have to change, later, as I remember, an endless chain.

What the game needs is logic in the right places. I mean, how can you build a ramp on the tower so that every IS fighter can come to you on foot or by car? How do IS fighters get onto the beach and attack you from behind? (translated)

Hello Pluschtiger,
A very big thank you for your very informative reply.
In fact so appreciated, that I will purchase the game.
Best regards,
A.

My pleasure. Tip before you buy it. Check out some more steam player videos. Especially since you see a little more there than in the shop. In guides you may also find how to get the updates that make the game more enjoyable for you the quickest. If you can wait wait for a sale, then the loss is not so big if it is not so convincing in the end. Otherwise, if you like games like this, in a recent discussion someone linked a similar one with WW2 environment (Normandy, D-Day). (translated)