Fix

conf/config.json

@@ -1,7 +1,7 @@
 {
     "default_server_config": {
         "m.homeserver": {
-            "base_url": "https://__DEFAULT_HOME_SERVER__",
+            "base_url": "__DEFAULT_HOME_SERVER__",
             "server_name": "matrix.org"
         },
         "m.identity_server": {

config_panel.toml

@@ -8,6 +8,6 @@ name = "Element configuration"
 
         [main.config.default_home_server]
         ask = "Choose a home server"
-        type = "string"
-        default = "matrix-client.matrix.org"
+        type = "url"
+        default = "https://matrix-client.matrix.org"
         bind = "base_url:__FINALPATH__/config.json"

manifest.json

@@ -41,13 +41,13 @@
 			},
 			{
 				"name": "default_home_server",
-				"type": "string",
+				"type": "url",
 				"ask": {
 					"en": "Choose a default home server",
 					"fr": "Choisissez un serveur par défault"
 				},
-				"example": "my-own-homeserver.tld",
-				"default": "matrix-client.matrix.org"
+				"example": "https://my-own-homeserver.tld",
+				"default": "https://matrix-client.matrix.org"
 			},
 			{
 				"name": "is_public",

scripts/upgrade

@@ -48,7 +48,7 @@ ynh_script_progression --message="Ensuring downward compatibility..." --weight=1
 
 # If default_home_server doesn't exist, create it
 if [ -z "$default_home_server" ]; then
-	default_home_server="matrix-client.matrix.org"
+	default_home_server="https://matrix-client.matrix.org"
 	ynh_app_setting_set --app=$app --key=default_home_server --value=$default_home_server
 fi