How you let customers make offers on their entire order depends on which version of Make an Offer you are using.
Latest Version (V2+):
You can allow customers to submit offers on an entire order by setting up an order rule:
Click the Rules link in the app navigation menu to go to the Offers page.
Click on an existing offer or create a new one.
In the Conditions section, under “Offer type”, select Order.
Click Save.
Legacy Version (V1):
If a customer submits offers on multiple products, you can combine them into a single order offer:
In the Make an Offer admin section, click Setup.
Select the Offers tab.
Find and accept the offer you want to work with.
If the customer has made more than one offer, you’ll see an option to combine those offers.
Select the offers you want to combine and click Yes.
In the next window, choose whether to accept or counter the combined offers.
Click Done.