XMLRPC was enforcing UTF8 for all the requests, enforces utf8mb4 for each queries like it is done in FlexiAPI (see https://github.com/laravel/framework/blob/v5.4.14/src/Illuminate/Database/Connectors/MySqlConnector.php#L55)

flexisip-account-manager.spec

@@ -8,7 +8,7 @@
 #%define _datadir           %{_datarootdir}
 #%define _docdir            %{_datadir}/doc
 
-%define build_number 75
+%define build_number 76
 %define var_dir /var/opt/belledonne-communications
 %define opt_dir /opt/belledonne-communications/share/flexisip-account-manager
 

src/database/database.php

@@ -46,7 +46,7 @@ class Database
               $this->conn = new PDO("mysql:host=" . DB_HOST . ";dbname=" . DB_NAME, DB_USER, DB_PASSWORD);
             }
 
-            $this->conn->exec("set names utf8");
+            $this->conn->prepare("set names utf8mb4 collate utf8mb4_unicode_ci")->execute();
         } catch (PDOException $exception) {
             Logger::getInstance()->error("Connection error: " . $exception->getMessage());
         }

src/objects/account.php

@@ -185,7 +185,7 @@ class Account
             $this->activated = "1";
             return true;
         }
-        
+
         Logger::getInstance()->error($stmt->errorInfo());
         return false;
     }