Ok, I redid all the steps as you mentioned, checked the VAT registration number, etc. but I still get the above screenshot

I did another check and our next VAT return is due in about 3 months. I have "The VAT Return dates are currently March, June, September and December" in HMRC so which month should I place in "When do you need to start calculating your VAT from?" of QB? I tried October but no luck