Troubleshooting

The preview says the package cannot be fetched

Check that:

the URL is a direct https://.../*.h5p URL;
opening it in a private browser window downloads the package or shows the archive response;
the file host permits cross-origin browser requests (CORS) from https://embed-my.github.io, the origin the frame runs on (Access-Control-Allow-Origin: * is the usual way);
the URL has not expired and does not require an LMS login.

Preparing and hosting packages lists the headers to set if you control the host.

The activity works in my LMS but not in Embed My

An export without its libraries normally plays anyway: the player takes the ones it needs from its own pack of the H5P hub's libraries, and upgrades content written for older library versions before it starts. Content made for a newer version than the pack has plays at the newest one it has, and the preview says so. If the preview still names missing libraries, the package needs one the pack does not carry: a new major version, or a library written for a single site. Re-export a complete package, including libraries. See Packages and library files.

An AR Scavenger activity shows only its title

The player does not run AR Scavenger. It writes its 3D and AR scripts into the page as inline scripts, which the frame's security policy refuses, so the activity shows its title and no scene, here and wherever the player runs.

The activity is cut off or leaves blank space

The resizer script from the generated snippet is missing or was stripped by your site. Use the platform's dedicated Embed, Custom HTML, or iframe block, which usually keeps scripts, or ask the site administrator to allow the script. If scripts cannot be used at all, the frame keeps the height the preview measured; raise the height in the snippet's style if the activity needs more room on your page.

A video is slow to start

The media is probably compressed inside the archive or not arranged for progressive playback. Ask the package publisher to run npx @missing-elements/h5p-normalize course.h5p. See Video that is slow to start.

The activity does not load in an app's built-in browser

Some in-app browsers give a frame no Service Worker, and the frame shows a link to open the activity on its own page. Share that link, or the page's own URL to open in a regular browser. Opened on its own, the activity plays without its package's own scripts, and its text keeps only the formatting its content type allows, as in an H5P plugin; one that needs its own scripts asks first and names the site it comes from.

Nothing plays on my page

Check that the page containing the iframe is served over https://. On http:// the frame has no Service Worker.

The host blocks the iframe

The site's Content Security Policy must allow frame-src https://embed-my.github.io. If it cannot, link to the activity's Embed My page instead: the src of the iframe in the snippet, opened on its own.

Reporting a problem

Open an issue where the problem lives:

The activity itself: it does not load, plays wrong, a content type misbehaves, a video is slow, the toolbar or fullscreen fails. That is the player, and its issues go to h5p-offline-player. Most reports end up here.
This website: the snippet it writes, the preview, the options, the page itself, and these guides: embed-my/website.
The frame itself, /h5p on embed-my.github.io, or the sizing script: embed-my/embed-my.github.io.

Not sure which? Pick the website; it will be moved. Whichever it is, include:

the page URL where the activity is embedded;
the package URL, if it is public;
the browser and version, and whether it is an app's built-in browser;
a screenshot or the visible error message;
whether the package worked from a local .h5p file or inside another platform.