The minimum Bugfender SDK version supported at the moment is 1.4.7.
Bugfender SDK version 1.9 works on iOS 10.0 and newer. For iOS 8 support you can still use Bugfender SDK version 1.8.
Please take into account, however, as iOS evolves and Apple stops providing support for older versions we will also drop support, since we can not do a reliable testing in old versions.
Dealing with older iOS versions
It is possible that Bugfender works in older versions too, please test extensively and use it at your own risk.
Even if Bugfender only works on modern iOS versions, you can integrate it in a project that supports older versions of iOS and just disable it for those versions. You can do that by configuring BugfenderSDK.framework as an Optional dependency.
Then, when you reference Bugfender in your code, you need to check if it's present, like this:
if ([Bugfender class]) {
// whatever you need to do
}