Price book items are matched from Housecall Pro to an already existing item in QuickBooks Online when an invoice syncs over that item to QuickBooks Online. This is done by clicking Finish, Invoice or Pay on a job in Housecall Pro.
During that sync, QuickBooks will try to find a match for the price book service entity, which includes the industry, and category. Housecall Pro queries QBO for all Items that have the same name and are under the same parent/category. For example, this ensures we do not link to "Remodel" under the “Kitchen” category, if it is supposed to under the “Bathroom” category, even though both categories have “Remodel” items. If no matches are found, the new price book item is created in QBO.
Material items will also match to items in QuickBooks, but only if listed in the same manner as it would push over from Housecall Pro, which shows as Price book Materials then the category: