Teddan did you run php flarum migrate after updating my extension prior to the Flarum 1.3.1 update?
For the error you see to happen, a different error probably happened the first time php flarum migrate was run after the extension update.
You can safely delete the url_hash column in the kilowhat_rich_embeds table to try again.
If a different error happens (like duplicate value insertion, or error creating index), can you share the error message and if possible a structure+data dump of the kilowhat_rich_embeds table?
There's a very tiny tiny tiny risk of generating conflicting hashes if you have a large number of entries in the table already. But this is incredibly unlikely.
If you have a lot of entries, the migration could also have failed due to timeout because it can take a lot of time to complete. Running the migrations via the command line should work around that issue.
