Sorry to hear your bun is poorly.
My two loved Septrin when they had it as it is usually banana flavour, they will both lick it from the end of the syringe!
Keep trying to tempt bunny with little tasty morsels and remove any uneaten foods often. I give little dishes dotted around with fresh herbs - basil, rosemary, sage, corriander, parsley, mint, grated carrot or apple (only a little of these as they are sugary) shredded greens, pellets, grass, dandilions.
I hope bunny is feeling better soon.