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Have you tried looking for "Publication Lists" in the SFMC documentation?
Publications lists are used for managing opt-ins and unsubscribes, they do not define the audience of your send. And if you don't have a specific publication list that you would like to use for a particular send, the All Subscribers list will be used. Here are more details ...
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as per your last comment / screenshot -
EazyE's original reply is correct, but your screenshot shows a misinterpretation of what was suggested. I'll try and elaborate.
ID_MKT_Cloud__c apparently is a field in your target DE.
The error tells you that in your target DE, it is in fact a mandatory field, so nothing can write data into the target without ...
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