The Actions button is grayed out preventing us from taking any action on the incomplete invoices

On the Payables invoices, Actions button is greyed out and not allowing to cancel the invoices. The invoices are in incomplete status. Kindly seeking your support for the following:

1. What could be the reasons for the ( Incomplete Status ) ?
2. Is there a way to activate the Actions button to allow us validate or cancel invoices
3. What would be the possible solution to clear / process the incomplete invoices ?