If you have been using a very old version of 1Password (version 3), it is not compatible with iOS releases of recent years, and will not run at all on iOS 11 or 12. Since iOS 9, we’ve been pushing out successive in-app warnings that a new version of 1Password is available. In iOS 10 our warning was more emphatic, urging you to upgrade immediately to avoid data loss. Unfortunately, if you’ve ignored these (and Apple's) warnings and upgraded to iOS 11 or 12, 1Password 3 will not open at all.
We don't have your data, but you may be able to recover it if you can confirm some preliminary requirements. Please read the following carefully and follow the instructions at the end:
When you initially began using 1Password 3 (the old version) on your iPhone, you were prompted to create a 4-digit unlock code and a Master Password (you may not remember creating a master password, but you did; otherwise, you would not have been able to use 1Password 3). If you think you know what it might be you can proceed with the recovery procedure, and, when asked for the Master Password, you can guess what you think it is. There is no penalty for guessing as many times as you like; you won't be "locked out."
iPad users: If you were using 1Password 3 on an iPad, then there is no 4-digit unlock code; instead, you had only a Master Password to unlock 1Password. If you know that, you can use it to recover your data.
1Password 3 will not open in iOS 11 or 12. However, you must be able to see (note the present tense) the 1Password 3 icon on your iOS device. If you delete 1Password, your data is gone. Reinstalling the app from the App Store will not restore your deleted data.
The icon looks like 'A' or 'B' in this image. You must be able to see that icon on your iOS device.
In order to recover data from your iOS device, you will need either a Mac with Yosemite or higher or a PC with Windows 7 or higher. If you don't have a computer of your own, you can borrow one from a trusted friend or relative.
And at the beginning of 2017, with plans to remove support for 32-bit apps (such as 2009's 1Password 3) in iOS, Apple added a warning when launching them, like this:
But since iOS 9, 1Password 3 has been warning users that it has been retired (since the release of 1Password 4 in 2012 it has not been under active development), with the latest coming:
1Password 3 Retired 1Password 3 is not compatible with iOS 11 or 12. To save your passwords and data, please upgrade now.
When you tapped "Skip", this message would appear again the next week; if you tapped "Later", it would appear again on the next launch; "Learn more" took you to instructions on our support site (iOS 10 or earlier) to migrate to a newer version, on iOS 9, 10, and 11 (1Password 6, or iOS 12 (1Password 7).
The icon for 1Password 3 will be either A or B, depending on the specific version you purchased: