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Issue picker uses an array of issue keys for storing its data: e.fg. ["PROJ-100", "PROJ-101"].
To set the values via the JIRA REST API you can set the array value directly, e.g. "customfield_10075": ["KAN-1963", "KAN-1957", "KAN-1730", "KAN-1958", "ASDF-18"].
If you want to set the values via .csv import, please use repeating columns for the values to be added:
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During the migration ( other formats (e.g. used by other issue picker apps ) might have to be converted into this format).
If issue keys change during migration (as is mostly the case), the old issue keys have to be replaced (mapped) with the corresponding ones used in the new instance so that the links still work.
Old Instance
1. Export Issues as CSV
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