I finally got the subscription screen in DTTG:
I really like that I got gently warned about the subscription, but I thought I had somewhere seen that for DTTG2 people there is an upgrade path. The screen above doesn’t list this,
Am I mistaken about an upgrade path?
There is an upgrade path; it relies on DTTG3 being aware of DTTG2 being previously installed on your device. I thought that it was sufficient for DTTG3 ever to have been opened when DTTG2 was still on the device. I may be mistaken, or maybe that just wasn’t the case in your case. Anyhow, if you put DTTG2 on your device (you will need to download it from your purchases rather than directly from the AppStore) and then open DTTG3 (you may either need to restart the iOS device, or open DTTG2 once first; perhaps you could post back here whether you had to do either of those things), you should be offered the lower one-time purchase price.
Yes, DEVONthink To Go 2.7.8 or 2.7.9 needed to be installed on the device at least once when you opened DEVONthink To Go 3. Version 3 then made a “mental note” of the presence of version 2. Maybe you removed version 2 already prior to installing version 3? In this case DEVONthink To Go 3 has no way of knowing that you’re an upgrader.
You can reinstall version 2 from your purchases in the App Store app to let DEVONthink To Go 3 know that you’re eligible. It will then offer you the discounted upgrade.
Thank you @Blanc and @eboehnisch! That was it!
I had never installed DTTG2 on this device.
Thx again, a great example of DEVONthink’s helpful support!
And BTW, your pricing is pretty reasonable - with and without upgrade discount. 
My free trial ended at the end of August and paid for version 3 on my iPad. All work as expeceted.
Started up DTTG on my iPhone today and the Retry/Restore does not work. It seems to want me to pay again…
No I am part of the beta program…So I was using V3 for quite a few months…All good on my iPad still!
Go into the iOS App Store > Your account > Purchased and try installing version 2. Then launch version 3.
Does that resolve it?
No. Still stuck at the screen asking to up upgrade or pay. Retry/Restore does not do anything. V2 seems OK with the Pro Package marked as Purchased. V3 does see the reduced rate upgrade by the way.
Again no issue on my iPad running iOS 15 beta!
Maybe on your iPad you used the sandbox account in iOS’ Settings > App Store to “pay” and on the iPhone you don’t? Sandbox “purchases” don’t carry over.
I do see a Sandbox identifier in the App Store setting on my iPad but I do not see this option at all in the setting on my iPhone. Any pointers…
