OCM uses the advertiser’s IAB category to perform “competitive separation” or “competitive exclusion”. This blocks multiple advertisers/brands that are competitive with one another from being served in the same ad marker when multiple ads are configured for one marker.

When creating a new advertiser, you can set the IAB category as seen below.

The unique combination of the category and sub-category need to be matched by another advertiser for category separation to occur. 

i.e. IAB13 - Personal Finance + IAB13-2 Credit/Debt & Loans is ONE category and competitive separation will only be performed if another advertiser has that unique IAB combination assigned as well.