Paypal gets the wrong amount value via the form - paypal

Question

In below code I send via a variable different amounts to Paypal when using this form. All data is correct even the amount is correct when Element inspecting via browser. But when Paypal site is active I always get 1 amount value USD25.00. It should be different for each $pitch->option_value.
Each variable $pitch->option_value is correct filled at my site. But Paypal only sees 25.
What do i do wrong or forget to do?
$i = '1';
foreach($pitches as $pitch) {
if($i == 1) {
$month = __('Month','agent-plugin');
} else {
$month = __('Months','agent-plugin');
}
$content .= '<form id="GotoPaypal" action="https://www.paypal.com/cgi-bin/webscr" method="post" target="_blank">
<input type="hidden" name="cmd" value="_xclick">
<input type="hidden" name="charset" value="utf-8">
<input type="hidden" name="return" value="'.get_home_url().'/en/my-account/">
<input type="hidden" name="item_name" value="'.$i.' '.$month.'">
<input type="hidden" name="amount" value="'.$pitch->option_value.'">
<input type="hidden" name="currency_code" value="USD">
<a href="#!" onclick="event.preventDefault();document.getElementById(\'GotoPaypal\').submit();">
</form>';
$i++;
}
return $content;

Answer 1

Because the value for $month will always be the same, no matter what value $i will have...
if($i == 1) { $month="25" } else { $month="25" }
will do the same trick ;)
You definded $i as somekind static value, why?