I am posting the following info on Hagia Sophia ticketing as I was otherwise unable to find it:
There is a QR Code outside Hagia Sophia which leads to the following link:
https://online.demmuseums.com/ (50€)
I personally thought this was the official one before I went and this is where I got my ticket:
https://istanbulwelcomecard.com/shop/hagia-sophia-tour (35€)
The downside of this website is they manually issue tickets during business hours. You have to buy it the day before, and in my case I had to text support ‘where’s my ticket’. They responded with my pdf ticket <30 seconds after that.
Reportedly the ticket office ticket is 25€. I think I recall the line looking tolerable when I showed up at 9am on a Monday.
Of course Hagia Sophia is undergoing renovations still and public visits happen from the upstairs gallery so the value is up to you, but it is still beautiful and historic.
Personally I found Nuruosmaniye Mosque even more compelling than Hagia Sophia. Please go if you have not.