What does the separator correspond to in the product ID of the feed?

If you export each product combination as a separated product in your Google Shopping feed, the product IDs in the feed are constructed like this:

(Prefix) + Product ID + separator + combination ID

Example: BT3v4

If you are using our Google Merchant Center (Google Shopping) module, or its Pro version, to export your product data to Merchant Center, then you don't need to specify the separator used, since the Google Dynamic Remarketing module will detect it by itself. But if you use another product export system, you must indicate the separator used in your feed, in the following option, so that it is taken into account by our module:

For example, if the IDs of your products (i.e. your product combinations exported as separate products) are of the form: 3-4 then you must indicate that the separator is a dash: