By default, Discount Ninja is configured to Disable quantity spinners of cart lines (and drawer cart lines) that contain free gifts added by the app.
This helps to avoid that customers can modify the number of free gifts in the cart.
You can, however, modify this setting. Go to Settings > Dynamic Pricing > Settings and click the "Quantity spinner" tab.
Note that Discount Ninja only affects the spinners of those lines that contain free gifts added by the app. Also note that, by default, Discount Ninja does not hide or disable the "remove" or "x" link available on a line on some themes.
Three options are available:
Theme default: this ensures Discount Ninja does not affect how the quantity spinners behave. The default behavior of your theme is therefore used, which typically means the spinners are visible and enabled. This allows customers to change the quantity of the line. If the customer
Hidden: hides the quantity spinner
Disabled: disables the quantity spinner (default setting)