Some drinks in the original set of recipes and some that I have personally made can't be added into the cauldron.
Some of the custom drinks can be added for some reason while others can't. Some of the original drinks also can be added while others can't.
In my case a custom recipe of Long Island cocktail included tequila, vodka, rum, gin, and a custom made triple sec. Only rum was unable to be added to the cauldron, and despite triple sec being a recipe added through config it worked fine and I was able to add it into the cauldron.

Version of minecraft is 1.17.1, and the Brewery is on 3.1

Problem solved.
When adding the ingredient in the config you have to write the name of the drink at its normal quality.
ex) name: Bitter Rum/Spicy Rum/&6Golden Rum > In this case you have to use 'Brewery:Spicy Rum'
At least it worked out for me.