When trying to insert an entity (user, heartbeats, ...) containing Unicode emojis, the following error is thrown.

[ERROR] failed to batch-insert heartbeats – Error 3988: Conversion from collation utf8mb4_0900_ai_ci into latin1_swedish_ci impossible for parameter

There are two reasons for this:

1. Depending on how and with what MySQL version you created your database, the tables' character set might not be utf8, but something like latin1 or so
2. The database connection uses utf8 character set, but not utf8mb. Accordingly, 4-byte characters (like 💩) can't be sent to the database