Halifax Clarity Card Interest and Cashback

I have a Halifax Reward Current account and Clarity Mastercard. Utilizing their Cashback Extras, I activated their 10% cashback for Harveys Furniture in August as I had seen a sofa that I wanted to buy. As the purchase would be over £1000, I opted to use the credit card to pay for the purchase online on 29th August 2017 and I am due £100 in cashback (I also used Topcashback and I am due another £82 - result!!)

As my statement has now been produced, dated 3 September 2017 it states that my next months estimated interest will be £16.85. Whenever I use the card, I pay it off in full before the statement is produced but I will not be able to do the same this time round.

My question is should I transfer the balance now onto my other card; I have Barclays Freedom Rewards with a minimal balance at 1.9% transfer fee and if so, would I jeopardise my cashback which is due to be paid this month.

As interest is being charged daily, I am quite keen to move the balance but not if it will affect the cashback. I have paid some off already and by the time the payment is due on 28 September, the balance remaining would be £800. If I transfer then, the fee would be £15.20 at 1.9%. I had planned on moving the balance anyway but I did not think about the cashback side of things.

Apologies if I have posted this in wrong place but as it involves my current account and credit card, I was unsure.

Thanks in advance!
HPG1