¿Why 'set()' function not works?

[AlexAntonioG]

Actually in my project i've been trying to send the event 'add_to_cart' but it doesn't work, this event executes through this flow :
User interacts in front -> the product it's added on the basket -> This send a request to the controller endpoint :

The controller route is this:

( This route it's encapsulated in it's group /landing/gtm/ )

Then, the controller function works like this:

And finally the function addToCart of service works like this:

The event doesn't work, the GTM tag is correctly defined because I inserted a dataLayer.push with test variables to test this event and Tag Assistant recognize it, but with set function doesn't work, I tried with the function on the controller but it is the same outcome as well.

I would appreciate any help you can provide me.