extraData is actually a string

CRM/Core/Payment/Stripe.php

@@ -642,7 +642,7 @@ class CRM_Core_Payment_Stripe extends CRM_Core_Payment {
       $stripePaymentIntent = new CRM_Stripe_PaymentIntent($this);
       $stripePaymentIntent->setDescription($this->getDescription($params));
       $stripePaymentIntent->setReferrer($_SERVER['HTTP_REFERER'] ?? '');
-      $stripePaymentIntent->setExtraData($params['extra_data'] ?? []);
+      $stripePaymentIntent->setExtraData($params['extra_data'] ?? '');
 
       $paymentIntentParams = [
         'paymentMethodID' => $paymentMethodID,

CRM/Stripe/PaymentIntent.php

@@ -35,7 +35,7 @@ class CRM_Stripe_PaymentIntent {
   /**
    * @var array
    */
-  protected $extraData = [];
+  protected $extraData = '';
 
   /**
    * @param \CRM_Core_Payment_Stripe $paymentProcessor

api/v3/StripePaymentintent.php

@@ -204,7 +204,7 @@ function civicrm_api3_stripe_paymentintent_process($params) {
   $stripePaymentIntent = new CRM_Stripe_PaymentIntent($paymentProcessor);
   $stripePaymentIntent->setDescription($description);
   $stripePaymentIntent->setReferrer($_SERVER['HTTP_REFERER'] ?? '');
-  $stripePaymentIntent->setExtraData($params['extra_data'] ?? []);
+  $stripePaymentIntent->setExtraData($params['extra_data'] ?? '');
   if ($setup) {
     $params = [
       // Optional paymentMethodID