Usually, for preventing duplicate entries we use data validation (countif or countifs).
if we need to entry same invoice number in second row, it should be allowed (with reference other cell)
Here, If there is a duplicate invoice number, it should not be allowed when typing, but by giving reference like ("allow"/"ok",/"accept") it should be allowed and in second row as i said above, Entry should be allowed by giving reference like ("continuous"/ "follows")
Being Prevention also it should be allowed, But By giving "text" references or any
Examle 123 - new
123 - continuous
123 - continuous
I think i explained good what i wanted
Thank You,