Navigate to the action menu on an account and select Internal Transfer to transfer cash between accounts. (the first example below shows a transfer between holdings account and the same owner).
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The list is filtered to show only the account that is owned by the user. To view, other account accounts remove the filer in Owner.
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The transfer order is now finished and can be viewed under on the account overview, on orders in the account overview, Internal Transfers, or navigate to Order Management > Transfer Orders > Internal Transfers.
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Example of cash transfer from ISK to ISK with the same owner:
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