Battleship VS crypto_vba

Then you need to do some research, otherwise you won't know what you're competing with! Take, the example, the version of Arkanoid made by VB6 developer - https://imgur.com/a/Z8GL0hk There are a number of projects on Github - like BattleShips by the maker of RubberDuck (the VBA Editor COM addin), Mathieu Guindon. You should check out Awesome VBA because there a few games listed to get you started.

It basically uses the Dictionary object to create variables (e.g. with a dictionary in a dictionary) and after that using that library to transform it into a string. I'm using it in my project here: https://github.com/krijnsent/crypto_vba/blob/master/ModExchKucoin.bas

I agree with u/sslinky84 that there is no safe place in VBA. The main question is: what's the purpose of an API key in this case? From your description you are not linking an API-key to a single user, but have "one key to rule them all". So you probably want to prevent someone from grabbing your end-point and spamming it? In that case you're perfectly fine in creating one API-string in VBA and checking that on the server: it blocks the person who is opening a browser to fiddle with your end-point, but it does give you some security. The people who can get through are the ones that manage to crack open your VBA (assuming you have a password on the VBA). To make their life a bit harder you could instead of a "fixed string" as API key go for some kind of hash, as u/archn suggests. E.g.: take the rest of the post message that e.g. also includes a mandatory timestamp, make a simple hash of that (might even include a "fixed key", see e.g. https://github.com/krijnsent/crypto_vba/blob/master/ModHash.bas for some code).

I've built an open source VBA-Excel library to communicate with cryptocurrency exchanges ( https://github.com/krijnsent/crypto_vba ) and have my code available as .bas and in an .xlsm file. A couple of days ago someone posted an issue that my xlsm file triggered a Windows defender alert. At my pc this doesn't happen, the AVG virus scanner also won't show anything.

I am mainly using Cryptocompare, but if you want to use CoinGecko, check out my code, it has the basics: https://github.com/krijnsent/crypto_vba/ It has most of the essentials: connecting Excel to web, handling Json and some API examples.