Hi
Standard NAV does not have approvals build into requisition worksheets, the req needs to first be converted in to a PO, and then the PO can be sent for approval
It is possible that this is a localisation done to your country specific version of NAV, but based on the fact that it does not work i will am pretty sure that those buttons were customization done by your NAV partner and they are not working
You will need to contact your partner to fix this development
Cheers
Nev