Determine the field in the original issue that will control the number of issues to be created. For instance, this could be one of the many Substitution variables that produce a comma-separated list like original_fixed_versions, role_developers, original_labels_comma_separated, or similar.
Determine any include or exclude criteria for subsetting the entries to be considered.
Determine if duplication prevention is needed and, if so, determine a condition that could be used to determine if the create should proceed. A JQL query is a convenient way to do this.
Configure the post function - see the example.
Example - Fix versions
Quote fix version fields that may contain blanks
What happens when there are no fix versions?
If the Create multiple issues field is replaced with blank or the regex eliminates all candidates, then no issues will be created.