If the number of leaf elements of the parent element in the source and target schema is same, then you can use Connect Mapping Children to map all the source elements to the corresponding target elements.
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When you define a Custom Auto Map, by default it is in deactivated state. To use a Custom Auto Map, you need to first activate it. Once you have activated the Custom Auto Map, you can use it in your mapping. Note that only activated Custom Auto Maps can be used in a mapping.
Steps to Activate a Custom Auto Map
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