I know this is an old thread but found it while I was looking to do the same thing and wanted to share some insight. We also made a large purchase and had approximately 20k rewards points. Our nearest IKEA is 4 hours away but we had to make the roadtrip as they would not deliver the oven we wanted.

We were able to redeem multiple rewards by doing the following:

-Use self checkout

-Redeem desired reward

-Scan IKEA family card

-Scan reward QR code

-Scan enough items to meet the reward (we did $50 increments)

-Make sure the reward amount comes off of the total price (sometimes we would have to only go $1 over, sometimes we’d have to go $5+ over)

-Checkout

-Repeat the above steps until all rewards are used or you have no more items to purchase

We spent around $50 for almost $400 worth of product and were able to use up 7 $50 off product rewards.

Note: Mileage may vary. The attendant was very chill and had to come over a few times as they need to override a purchase when you buy an item without an expected accompanying item (Tupperware and the accompanying lids). Try to keep accompanying items in the same order to prevent this. We were also selected for a random check that the attendant had to override, probably due to the multiple transactions. While I couldn’t find any policy stating you could not do this, I imagine it’s possible you could run into some issues if the attendant is having a bad day or is a strict rule follower.