revert: remove testmode parameter from Mollie payment creation

Removed the testmode parameter as it was causing issues. Mollie will
automatically determine test/live mode based on the API key used.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/providers/mollie.ts

@@ -17,13 +17,6 @@ import { createContextLogger } from '../utils/logger'
 const symbol = Symbol.for('@xtr-dev/payload-billing/mollie')
 export type MollieProviderConfig = Parameters<typeof createMollieClient>[0]
 
-/**
- * Determine if testmode should be enabled based on API key prefix
- */
-function isTestMode(apiKey: string): boolean {
-  return apiKey.startsWith('test_')
-}
-
 /**
  * Type-safe mapping of Mollie payment status to internal status
  */
@@ -168,9 +161,6 @@ export const mollieProvider = (mollieConfig: MollieProviderConfig & {
       validateProductionUrl(redirectUrl, 'Redirect')
       validateProductionUrl(webhookUrl, 'Webhook')
 
-      // Determine testmode from API key (test_ prefix = true)
-      const testmode = isTestMode(mollieConfig.apiKey)
-
       const molliePayment = await singleton.get(payload).payments.create({
         amount: {
           value: formatAmountForProvider(payment.amount, payment.currency),
@@ -179,8 +169,7 @@ export const mollieProvider = (mollieConfig: MollieProviderConfig & {
         description: payment.description || '',
         redirectUrl,
         webhookUrl,
-        testmode,
-      } as any);
+      });
       payment.providerId = molliePayment.id
       // Use toPlainObject if available, otherwise spread the object (for compatibility with different Mollie client versions)
       payment.providerData = typeof molliePayment.toPlainObject === 'function'