The add to cart event does not appear in the datalayer.
I can’t even figure out what the problem could be.
I use your plugin on other sites and it works.
The strange thing is that the begin_checkout and purchase events work correctly instead
Most likely, it is a custom add to the basket flow/function/plugin and is not tracked by standard WP methods. The simplest solution is to add your own dataLayer.push for this event with parameters and use it. This is usually a fairly simple task for developers, but just in case, here is some general documentation about the data layer: