Step 1: Open the program and press "Install".

Step 2: Get an error.

Step 3: Press Win + R.

Step 4: Enter "%localappdata%" in the field and press Enter.

Step 5: Find a "MegaHack" folder and follow the path "Install > Mega Hack Pro > v8.0-alpha", where should the file be download.zip.

Step 6: Move all files from download.zip to folder with your Geometry Dash.

Enjoy!

thx weebify for this guide