For a recently updated CiviCRM 5.56.2 + Drupal 7 (using mariadb 10.3), I got the little black box with the message "DB Error: unknown error" popping up when trying to send a mosaico civimail (e.g. as a test).

Weirdly, there was nothing helpful in the CiviCRM error log or the Drupal error log, or the sql error log or the apache error log!

I eventually discovered the error message in the browser console, which now makes some sense (since mosaico does a whole whack of js api stuff).

The error was hard to figure out because it was full of a long string it had pulled out of the civicrm_mailing table, but if I look far enough, I can see this:

Illegal mix of collations (utf8_unicode_ci,IMPLICIT) and (utf8mb4_general_ci,COERCIBLE) for operation '=']","type":"DB_Error"

I'm not seeing this in other updated sites (or at least, not yet ...), and I had run

cv api System.utf8conversion

Anyone with a similar experience or clue?

  • The api call doesn't update extension tables if they don't start with civicrm. If that's the problem, then you need to add the patterns=table1,table2 parameter.
    – Demerit
    Jan 9, 2023 at 16:19
  • Good point, though not this issue.
    – Alan Dixon
    Jan 9, 2023 at 21:02

1 Answer 1


I reran cv api System.utf8conversion and now it works.

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