Show different button text if no content

First off, as I mentioned in the comment, you got a syntax error here, where there’s an unwanted }:

$meta = get_post_meta( $post->ID, 'clpr_coupon_code', true );} // <- that }

(Updated answer — Previous code were removed since they didn’t work for you.)

So if you want to show the special text when $clpr_options->coupon_code_hide does not evaluate to a true and that the field clpr_coupon_code is empty; try this:

<?php if ( $clpr_options->coupon_code_hide ) {
    $class .= ' coupon-hidden';
    $meta = get_post_meta( $post->ID, 'clpr_coupon_code', true );

    // If clpr_coupon_code is empty.
    if ( ! $meta ) {
        $button_text="Angebot anzeigen";
    // If clpr_coupon_code is not empty.
    } else {
        $button_text = fl_get_option( 'fl_lbl_show_coupon' );
        $button_text="<i class="icon-lock"></i>" . $button_text;
    }
}
?>