When user clicks a category from the offer sidebar, this page opens. Two filter sidebar approaches.
Offer-branded banner at top, price range + brand + attribute filters in sidebar, product grid with sort. Filter data pulled live from products in the group.
No sidebar. Banner at top with coupon. Filter chips across top (dropdown on click). Wider 4-col product grid. Cleaner, more modern feel.
Both options: back link to offer, product count, sort. Filters pulled from actual products in the group (brands, price range, attributes from OpenCart product fields).