Some features on Yoyo Chinese, like flashcard practice, quiz, mastery review, etc., use audio auto-play so that you don't have to click a button each time you want to hear the audio.
Your browser may have audio auto-play disabled already by default and/or need to be enabled in order to use these features as intended.
Additionally, mobile browsers have finicky rules about audio auto-play and require the user (that's you!) to have interacted with the website in certain ways before the browser will allow & enable audio-auto play.
See below for details on how to enable audio-auto play in each browser and keep in mind that if you're on mobile, you may also have to click a few audio files and use the site for a few minutes before the audio-auto play will start working.
In the Safari app on your Mac, choose Safari > Settings for This Website.
Hold the pointer to the right of Auto-Play, then click the pop-up menu and choose the option Allow All Auto-Play
When Firefox is actively blocking media on a website, you'll see a special icon in the address bar.
Click that icon to open the Site Information drop-down panel, where you can change the Autoplay setting for that website.
Click the icon to the left of the address in your URL bar and choose Site Settings.
In the Permissions section under Sound, change the setting to Allow.
Click on the three-dot menu for options.
Select Settings from the list.
Switch to the Site Permissions from the sidebar menu.
Scroll down and choose the Media autoplay option within Site permissions.
From the drop-down choose the Allow option.