Update packages/fints/src/dialog.ts

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: larsdecker

packages/fints/src/dialog.ts

@@ -282,8 +282,17 @@ export class Dialog extends DialogConfig {
      * @see https://www.hbci-zka.de/ for FinTS specification
      */
     public async handleDecoupledTan(
-        transactionReference: string,
-        challengeText: string,
+        // Ensure TAN methods are available before attempting decoupled TAN handling
+        if (!this.tanMethods || this.tanMethods.length === 0) {
+            throw new Error(
+                "No TAN methods are available for decoupled TAN handling. " +
+                    "Ensure the dialog is properly initialized and TAN methods have been retrieved.",
+            );
+        }
+
+        // Find the appropriate TAN method (prefer one with decoupled support)
+        const tanMethod =
+            this.tanMethods.find((m) => m.decoupledMaxStatusRequests !== undefined) || this.tanMethods[0];
         statusCallback?: DecoupledTanStatusCallback,
     ): Promise<Response> {
         // Find the appropriate TAN method (prefer one with decoupled support)