Add amount in purchase invoice discount?

How can I add amount in purchase invoice discount column instead of %?

If the discount is fixed amount rather than percentage, simply click Add line button to add another line item and enter negative amount which should represent the discount.

If we do that, the discounted amount is shown in suspense account.
What should we do then?

The discount line item must be allocated to an account such as Discounts applied that you create for this purpose. This must be an expense account. It will reduce your net income by offsetting the revenue from the full-price line item.

Suspense is an account Manager uses to store incomplete, incorrect, or unbalanced transactions until you can fix them. It should always be zero.

So, in case of Sales Invoice, we need to create “Discount Applied” under “Expense”.
Got it.

What account should we create for discount in purchase invoice?

See my answer to your other post. There may not be a need to create any account for purchase discounts. Just lower the price according to the discount.