Support

Thank you for the more specific information, I can not understand the situation better!

This is a Joomla bug. The following procedure only applies to Joomla 3 and Akeeba Backup 8 — that's why I needed the version numbers!

1. Go to Extensions, Manage, Update Sites.
2. Search for Akeeba Backup.
3. Select all items on the list and click on Delete.
4. Go to Components, Akeeba Backup.
5. Click on Options, Live Update and remove the Download ID.
6. Click on Save & Close.
7. Click on Options, Live Update again, this time entering your Download ID.
8. Click on Save & Close again. Please note that the last four steps are NOT redundant and must be carried out at exactly this order, without doing anything else in between.
9. Then go to Extensions, Manage, Update and click on Clear Cache.
10. Go to System, Clear Cache. Select Administrator from the drop-down and click on Clear All.
11. Go back to to Extensions, Manage, Update and click on Clear Cache again.
12. Now click on Find Updates.

Now let's see why that works.

You had Akeeba Backup Core installed on that site and then installed Akeeba Backup Professional. There are two discrete issues in Joomla:

• Joomla is supposed to remove the Core update site and install the Pro update site when you upgrade from Core to Pro. Because of a bug — the existence of which is confirmed as of late January 2022, eight years after I first reported it, but the actual trigger is not yet discovered — Joomla sometimes thinks the update is not an update(!) and doesn't modify the update site, doesn't copy all files, does not update its cache of the package extension's XML manifest, does not delete the XML manifest of Akeeba Backup Core or does a combination of the above.
• If you use the Rebuild button in the Update Sites page Joomla uses its cached information for the package extension's XML manifest. Because of the bug above it may pick up the manifest of Akeeba Backup Core (which is no longer installed on your site but Joomla doesn't actually know that's the case because its cache is borked!) and install the update site for Akeeba Backup Core.

Steps 1 to 3 remove the wrong update site.

Step 4 reinstalls the correct update site but because of another Joomla issue that has to do with how it caches component options (even when Joomla's cache is disabled!) you may end up with an update site to the Professional version which does not have the Download ID applied to it.

Steps 5 to 8 are NOT redundant. They address the problem described above. Steps 5 to 6 bust the Joomla component options cache but also mean that you do not have the Download ID at all. Steps 7 and 8 re-establish the download ID, bust the component options cache once again and apply the download ID to the update site for the Professional version.

Normally, you'd think you're done. However, the caching issue extends to how Joomla lists and finds updates (thankfully, this WAS fixed in Joomla 4 after the fifth time I explained to a core maintainer how it happens, it was an one line fix, something which should have been done eight years ago; better late than never). So, steps 9 to 11 try to get Joomla to bust that cache. 

Only at this point you can search for updates again, using the correct update site and correct download ID, hence step 11.

Joomla 4 addresses most of those issues. It may still find the wrong update site but you can delete just the one wrong update site and enter the correct Download ID directly into the Update Site itself, without having to go through the component. The component options caching is irrelevant. Moreover, the Updates page is reworked so that the button to Clear Cache actually does clear cache instead of going halfway there. So if you were on Joomla 4 you'd have different steps, with a slight variation depending on whether you were using Akeeba Backup 8 or 9. And now you know why I was insisting on the exact version numbers. Trying to work around what's broken in Joomla requires knowing which Joomla version we're dealing with and whether the Download ID is applied by the component (Akeeba Backup 8) or directly in the update site (Akeeba Backup 9).