Need to apply additional promotion codes for promotional goods items

Dear Team,

We have defined a line group level -promotional goods modifier.which will default promotional item on sales order

For Example : if item A enter on sales order item B will be added on sales order with price of 10

in this scenario item A price would 15$ and item B price would be 10$

Once order entered if the customer is eligible for further discount ,booking agent will enter promo code at line level

Item A we are able to enter promotion code at line level,But for item B we are unable to enter promotion code as we don't find any promotional codes are listed out