In order to approve MRN's you must assign as MRN requested Location approve user.
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Step 03 : After opening MRN you can view MRN containing items as below, you can identify new items by Item “No” empty lines for those you need to check “New Item Verify” tick box. For other items you can site stock if exist and you need to tick “Site Stock Verify” tick box as below also you can change required Quantity by changing “Quantity”;