How to change invoice amount on unpaid invoice.

I want to change an invoice amount, the invoice is unpaid and status is in Needs Revalidation due to hold on it. The invoice amount field is grayed out.

I updated invoice amount in ap_invoices_all now the header amount and distributions amount matches, but when i look into Scheduled Payments tab i see the payment schedule Gross Amount which i then changed, then right below there are two sections Payment Schedule and Invoice, the value in Amount Remaining , Gross Amount and Gross Amount Total got changed the Invoice Amount remains the same old value which then throws below error.