You can’t upgrade from 7.1 to 8.9.6 directly. First you need to upgrade to SonarQube 7.9.6 (the former LTS version) and then upgrade to 8.9.6 (the current LTS).
(…) However, if there are one or multiple LTS versions in your migration path, you must first migrate to each intermediate LTS and then to your target version, as shown in Example 3 below.
Example 1 – From 8.1 > 9.0, the migration path is 8.1 > 8.9.1 LTS > 9.0 Example 2 – From 8.2 > 8.9 LTS, the migration path is 8.2 > the latest 8.9 LTS patch. Example 3 – From 6.7.7 LTS > 8.9 LTS, the migration path is 6.7.7 LTS > 7.9.6 LTS > the latest 8.9 LTS patch.