Gtin Export To Gmc Feed Problem

Hi,

I have problem with export GTIN to XML. I crteate it like

...

[P_PRODUCT_IMAGE]
[P_PRODUCT_PRICE]
[P_PRODUCT_GTIN]
new
[P_PRODUCT_ID]-[P_PRODUCT_CODE]
...
I have the GTIN field filled on the product features page. Unfortunately, I don't see these values in XML. I don't have GTIN in documentaries. Can someone help me?