WTF

Sorry, but this is really shitty plugin. Caused me to waste few hours to find why it’s not working while returning error about token.

Hell why did you commented scripts action?

// load frontend scripts

// add this action when the payment form is viewed
// add_action('wp_enqueue_scripts', 'paymill_load_frontend_scripts');
// or if above doesn't work, try this:
// paymill_load_frontend_scripts();

Did you wrote it yourself or just copy-pasted code found in Google?

Also there’s an invention called “space” – it’s a big horizontal bar on your keyboard and it’s used to put actual space into the code to make it a little more readable.