Installation guide

About two minutes, and you only do it once — later updates are simply opened like any other file.

1. Download the file

Once payment succeeds you receive an email with a download link and your licence key. Open that link directly on the Android phone the child will use.

The file ends in .apk. Your browser may ask "Save file?" — choose save. If a warning appears saying this kind of file can harm your device, that is the standard sentence Android shows for every apk, not a judgement about ours.

2. Check the fingerprint (optional, but worth it)

We publish the SHA-256 fingerprint of every release file on the home page. If you want to be certain the file in your hands is the one we published — rather than a copy someone else has altered — compare the fingerprints.

On the Android phone — the sensible route, since that is where the file was downloaded. Install any hash checker from the Play Store (search "hash checker" or "SHA256"), open the apk with it, and pick SHA-256.

On Windows, open PowerShell in the download folder and run:

• Get-FileHash file-name.apk -Algorithm SHA256

Compare the result with the one on the page. Ignore spacing and letter case: we print it in eight lowercase groups so it can be read, while most tools return a single uppercase line. What must match is the 64 characters, in order. If even one differs, do not install it — contact us instead.

3. Allow installing from this source

Tap the downloaded file. Android will stop you here and say something like: "For your security, your phone is not allowed to install unknown apps from this source."

Tap Settings in that dialog and switch on Allow from this source. You are granting it to the app the file was opened from — usually Chrome or your file manager — not to the whole phone. Press Back and the installation continues.

Afterwards you can switch that permission off again if you prefer. An app that is already installed keeps working.

4. Paste the licence key

Open Monstermath. On first launch, paste the key from your email. It is long — around a hundred characters — and it is meant to be copied and pasted, not retyped.

If your email client breaks it across several lines, that is fine: the app ignores spaces and line breaks. What matters is that every character comes across, including the dot in the middle.

No internet is needed for this step. The key is checked inside the phone — there is no other way it could work, since the app holds no internet permission at all. You can activate it in aeroplane mode.

If something goes wrong

"App not installed"

Usually an older version is still installed with a different signature, or storage is nearly full. Uninstall the old version, make sure there is around 100 MB free, and try again.

The file will not open after downloading

The download may have been cut off partway. Delete it and download again on a stable connection. The correct file size is stated in your email.

The licence key is rejected

Almost always because a character did not come across. Select the key from the very start to the very end — including the dot in the middle — and copy it again. Do not retype it: a zero and a capital O, a one and a lowercase L, are easy to confuse, and the key was never designed to be typed.

If it is still rejected, send us the key on WhatsApp and we will check it.

The child has been using it and you change phones

Install as normal on the new phone and paste the same key. If Google Backup was enabled on the old phone, the child's progress usually restores by itself.

Installing updates

We email you whenever a new version ships, with the download link and its new fingerprint. Download and open it as before — it installs over the old version and the child's progress is not erased. The licence key does not need to be entered again.

The app does not update itself and never checks for new versions in the background. Without the internet permission it could not — and that is deliberate.