Releasing PO second time in ME28

Hi Experts,

The PO is approved in ME28 for the first time in the transaction code ME28. After approving the PO, changes are made later to the purchase order, which will again reassign the release strategy. This purchase order will again appear in the ME28 list for the approval, since this was already approved in ME28 and this purchase order is appearing for the second time in ME28 but without the release button (green tick mark and pencil icon). However this release button is available in T. code ME29N.

Why this release button is missing in T. code ME28 but it is available in T. code ME29N ? The approver would like to release the PO through the T. code ME28.

Many Thanks in advance.

Regards

LYD