Can you confirm that you have added
promotion_item to Searchable Atributes & Attributes for Faceting? See screenshots below:
The specific search I used with a similar sample dataset was:
"filters":"promotion_item:1 AND price:10 TO 20"
You can also accomplish it with:
"numericFilters": ["price:10 to 20"]
Let me know how it goes and if you have further questions.