One thing you can do is understand the visitors' behavior. Like what makes them leave the website, what makes them buy something.
Before you start complaining about the complexity to do this thing, let me introduce a software called Enhencer. What it does is after integrating a Custom GTM based API, Enhencer will automatically collect the visitors' data from the website and predict their likelihood to buy something on a real-time basis. Enhencer does that using AI algorithms.
Once you know which customers are more likely to buy something, you can engage them with promotions and coupons, and something like this. The idea is to engage them so that you can secure that possible sale. Again, you need to know which customers are more likely to buy something rather than simply randomly handing them promotions.
The key point of this is: Enhencer will automatically provide you a real-time prediction on the website visitors, without any human interventions and complexities. All you have to do is integrate the first API and later provide promotions to the higher likely visitors. This will not magically increase the sales and conversion overnight, but this will help you to secure that next possible sale and over time you will increase the website conversion bit by bit.
Enhencer also has a free plan and trial versions. Check them out and see how they actually do this: https://enhencer.com/