Could an invalidated invoice be paid? If no, then what is the significance of applying a hold on an invoice at a supplier level to INVALIDATED?

only validated invoices could be paid.
an invalidated invoice could be made validated (after fixing problems) and eventually paid.

To apply an Amount Hold and Unmatched Hold on invoices at a supplier level makes sense to me. But, to apply Invalidated Hold on invoices at a supplier level does not make sense to me, since all invoices would any way be validated before they can be paid.

Step 1 - You enter invoices first.
Step 2- Then you validate invoices that you have entered (you can do that in a batch by running validation program).
Step 3- Then you pay the validated invoices.
Lets say we have a dispute with a supplier and the management decided to hold all those invoices that are still on step 1 (entered but not validated) but not the invoices that are already validated (step 2). This type of functionality comes handy.
Oracle caters to all kind of different requirements. Not all functionality has to be used to every one.

Step 1 - You enter invoices first.
Step 2- Then you validate invoices that you have entered (you can do that in a batch by running validation program).
Step 3- Then you pay the validated invoices.
Lets say we have a dispute with a supplier and the management decided to hold all those invoices that are still on step 1 (entered but not validated) but not the invoices that are already validated (step 2). This type of functionality comes handy.
Oracle caters to all kind of different requirements. Not all functionality has to be used by every one.

I got it now. Thank you, Hasan.

Invoice validation will trigger the hold,invoice validation does all the checks neccesary, eg suppliers,distributions,headers and line amounts. etc.Invoice must be validated then accounted