Whats the difference between giving evidence in Merit hearing vs adjudicative hearing

Whats the difference between giving evidence in Merit hearing vs adjudicative hearing??/

(i recently had a adjudicative hearing i gave all my evidence infact for more than 1 year prior and present so they told me to amend application and only give evidence from may 2024 to 2025) So my question is why is there a merit hearing (evidence) if on the application it said i must give evidence in the adjudicative hearing...