Selling unique products and NO GTIN
1. Sign to your Google Merchant account here.
2. From your dashboard, go to Products, then Feeds
3. At your Feeds page, click the feed your want to edit. For the image below, our feed is Content API.
4. In your Feed page, click Feed rules. See image below as reference
4. Click the plus button to add a feed rules, and type Identifier exists, then click the identifier exist under Processed attributes. See image below
5. Next, under the Data Sources, click the Add Source then Conditions: None, then type gtin and click the gtin under the Processed Attributes.
6. Click the contains and change it to has no value.
7. Click Set to, then under Typer or select, click Add value, then select No.
Settings should be as follows, see image below
Changes to your google merchant might take some time.