SHA-and-HMAC VS Chatterbox

JujuAdams/Chatterbox which PowerPlaidPlays mentioned in his comment may appear in your search results. friendlycosmonaut/Dialogue-System is at the top of my search results. I could see a few others - nothing wrong with more references, right? Just pick your favorite implementation, design pattern, or coding style.

use the free system already provided by the great and generous jujuadams: https://github.com/JujuAdams/Chatterbox

if your game is dialog heavy i'd recommend looking at this: https://github.com/JujuAdams/Chatterbox

Here's a link to a better branching narrative solution: https://github.com/JujuAdams/chatterbox

Note: Found where the error might be. Although I disagree with how he is approaching branching dialogue systems, I understand you are still learning. When you feel more comfortable with GameMaker, I recommend checking out JuJu Adams free extension called Chatterbox

I'd also recommend Chatterbox. First of all there are some really good editors for YARN Files out there (with visual representation of the dialog s, like this one) and it's easy to add functions to the yarn script (for example if you reach a certain point of a dialog you can change a flag or add an item to the inventory).

I haven't used it personally, but Jujuadams made Chatterbox which should effectively do exactly what you're looking for.