Does it happen after a good amount of time? Free usage of our API is limited to 1,000 API requests per day. If you exceed 1,000 requests in a 24 hour period we'll return a 429 HTTP status code to you. I think you may be json_decoding an error and that's why facing the non-existing property error. There seems to be nothing wrong as per the information you provided.
PHP: [16:35:41] [Server thread/CRITICAL]: Could not pass event 'pocketmine\event\player\PlayerJoinEvent' to 'PlayerLoggerInfo v1': Cannot use object of type stdClass as array on ArmTheDev\ArmTheDev [16:35:41] [Server thread/CRITICAL]: Error: "Cannot use object of type stdClass as array" (EXCEPTION) in "PlayerLoggerInfo_v1/src/ArmTheDev/ArmTheDev" at line 42 [16:35:41] [Server thread/DEBUG]: #0 src/pocketmine/plugin/MethodEventExecutor(38): ArmTheDev\ArmTheDev->onPlayerJoin(pocketmine\event\player\PlayerJoinEvent object) [