diff --git a/src/stripe/internal/constants.ts b/src/stripe/internal/constants.ts
new file mode 100644
index 00000000..af293921
--- /dev/null
+++ b/src/stripe/internal/constants.ts
@@ -0,0 +1,7 @@
+/**
+ * Stripe API version with `.preview` suffix.
+ *
+ * Required for `shared_payment_granted_token` (SPTs are in private preview).
+ * Bump this when upgrading to a newer Stripe API version.
+ */
+export const stripePreviewVersion = '2026-02-25.preview'
diff --git a/src/stripe/server/Charge.ts b/src/stripe/server/Charge.ts
index 89bfce5d..cef42abe 100644
--- a/src/stripe/server/Charge.ts
+++ b/src/stripe/server/Charge.ts
@@ -5,6 +5,7 @@ import type { LooseOmit, OneOf } from '../../internal/types.js'
 import * as Method from '../../Method.js'
 import type * as Html from '../../server/internal/html/config.ts'
 import type * as z from '../../zod.js'
+import { stripePreviewVersion } from '../internal/constants.js'
 import type {
   StripeClient,
   CreatePaymentMethodFromElements,
@@ -202,13 +203,16 @@ async function createWithClient(parameters: {
         // `shared_payment_granted_token` is not yet in the Stripe SDK types (SPTs are in private preview).
         shared_payment_granted_token: spt,
       } as any,
-      { idempotencyKey: `mppx_${challenge.id}_${spt}` },
+      { idempotencyKey: `mppx_${challenge.id}_${spt}`, apiVersion: stripePreviewVersion },
     )
     // https://docs.stripe.com/error-low-level#idempotency
     const replayed = result.lastResponse?.headers?.['idempotent-replayed'] === 'true'
     return { id: result.id, status: result.status, replayed }
-  } catch {
-    throw new VerificationFailedError({ reason: 'Stripe PaymentIntent failed' })
+  } catch (error) {
+    const detail = error instanceof Error ? error.message : String(error)
+    throw new VerificationFailedError({
+      reason: `Stripe PaymentIntent failed: ${detail}`,
+    })
   }
 }
 
@@ -240,11 +244,25 @@ async function createWithSecretKey(parameters: {
       Authorization: `Basic ${btoa(`${secretKey}:`)}`,
       'Content-Type': 'application/x-www-form-urlencoded',
       'Idempotency-Key': `mppx_${challenge.id}_${spt}`,
+      'Stripe-Version': stripePreviewVersion,
     },
     body,
   })
 
-  if (!response.ok) throw new VerificationFailedError({ reason: 'Stripe PaymentIntent failed' })
+  if (!response.ok) {
+    const body = await response.text().catch(() => '')
+    const detail = (() => {
+      try {
+        const parsed = JSON.parse(body) as { error?: { message?: string } }
+        return parsed.error?.message ?? body
+      } catch {
+        return body
+      }
+    })()
+    throw new VerificationFailedError({
+      reason: `Stripe PaymentIntent failed: ${detail}`,
+    })
+  }
   // https://docs.stripe.com/error-low-level#idempotency
   const replayed = response.headers.get('idempotent-replayed') === 'true'
   const result = (await response.json()) as { id: string; status: string }
diff --git a/test/html/server.ts b/test/html/server.ts
index 13d52c7e..2483ef5b 100644
--- a/test/html/server.ts
+++ b/test/html/server.ts
@@ -6,6 +6,8 @@ import { generatePrivateKey, privateKeyToAccount } from 'viem/accounts'
 import { tempoModerato } from 'viem/chains'
 import { Actions } from 'viem/tempo'
 
+import { stripePreviewVersion } from '../../src/stripe/internal/constants.js'
+
 export async function startServer(port: number): Promise<HtmlTestServer> {
   const stripePublishableKey = process.env.VITE_STRIPE_PUBLIC_KEY
   const stripeSecretKey = process.env.VITE_STRIPE_SECRET_KEY
@@ -190,6 +192,7 @@ async function createSharedPaymentToken(request: Request, secretKey: string): Pr
       headers: {
         Authorization: `Basic ${btoa(`${secretKey}:`)}`,
         'Content-Type': 'application/x-www-form-urlencoded',
+        'Stripe-Version': stripePreviewVersion,
       },
       body: bodyParams,
     })