jordanjay29 HieuYTB Flarum extensions are installed using Composer (which is our recommended method for installation, too). Can you tell me which extension you're trying to install? And how you installed Flarum?
jordanjay29 HieuYTB How did you install Flarum then? Adding extensions is going to be difficult for you if you do not have access to SSH. Did you by chance use Pockethold or another installation method with Bazaar included? If so, you can use Bazaar.