Moodle 4.1.6, recently migrated from Windows/PHP 7.4/MSSQL to RHEL9/Apache/PHP 8.0 w/ FPM/MySQL.  A user who is a Site Admin attempts to send a message to an individual user and intermittently receives a red webservice/formatnotsupported display along with a retry link. This is followed by a generalexceptionmessage "core_message_external::get_conversation_messages(): argument #2 ($convid) must be of type int, null, given, called in dirroot/lib/externallib.php on line 262." The retry action worked after multiple attempts but may be creating individual message IDs in mdl_messages.