Invoice Validation button should be grayed out/disabled if Invoice is not Approved

Summary:

Invoice Validation button/task should be grayed out/disabled if Invoice is not Approved

Content (required):

Business requirement to grayed out Validation option until unless invoice is approved. We have tried with option "Require validation before approval" but this option allow us to initiate approval for both invoices which are in Validation/not validated status. Do we have any option to meet my requirement through Sandbox? Tried with sandbox invoice status but not finding Invoice approval status Binding parameter.

I can create separate role and assign to the user but same person should not have this role. Business needs to same person should initiate approval, once invoice is approved and he need to validate.