commerce – Stripe php implementation

I tried to install the Stripe module to use it in my commerce shop on my Drupal 9 site. However, this yielded many errors so I decided to implement Stripe using php and based on this tutorial :
Everything works fine. But I have a small question. My payments are in euros and I don’t want to put the following hidden mentioned in step 2.

<input type='hidden' name='amount' value='0.5'> <input type='hidden'
        name='currency_code' value='USD'> <input type='hidden'
        name='item_name' value='Test Product'> <input type='hidden'
        name='item_number' value='PHPPOTEG#1'>

So I decided to put instead :

$total_price = $order->getTotalprice()->getNumber();
$currency_code = $order->getTotalprice()->getCurrencyCode(); //which is in euros for all orders

$_POST('amount') = $total_price;
$_POST('currency_code') = $currency_code;
$_POST('item_name')  = 'Order' ;
$_POST('item_number') = $order_number;

The result was successfully displayed in my Stripe Dashboard within the all payments section.
My order total is 12.5 euros. So I got 12.5 Euros (EUR) in my dashboard all payment section.
However, in the all transactions tab, I got net: 14.32 $ , amount : 15.06 $ , fee : 0.74 $ and a date that is in the future ! In addition to that 15.06 $ does not correspond to 12.5 euros because, in the Stripe conversion estimate page 12.5 euros yielded 15.21 $.
Is there anything wrong in what I did ??