Welcome bigal!
Does the cutting look ok above the soil also, or does it look dried out?
I am a rookie with cuttings, but one trick I tried this year with some cuttings that never rooted after 4-8 weeks in potting mix, in perlite or in the towel-in-Baggie methods was to put the cuttings upright in a tall cup of hot water direct from faucet, as hot as possible, then let that cool down and sit for 4-8 hrs. A number of those cuttings then started roots pretty fast when put into moist perlite again
Good luck