fix: correct Mailgun API URL and enhance error handling in MailgunAccount class

- Fixed the incorrect API URL in MailgunAccount class.
- Improved error handling for email sending failures by providing detailed error messages based on response content.
- Updated test file to export the tap.start() function for better module integration.

ts/mailgun.classes.account.ts

@@ -18,7 +18,7 @@ export class MailgunAccount {
     this.apiBaseUrl =
       this.options.region === 'eu'
         ? 'https://api.eu.mailgun.net/v3'
-        : 'https://api..mailgun.net/v3';
+        : 'https://api.mailgun.net/v3';
   }
 
   /**
@@ -127,8 +127,24 @@ export class MailgunAccount {
         );
         return await response.json();
       } else {
-        console.log(await response.json());
-        throw new Error('could not send email');
+        let errorMessage = `HTTP ${response.status}: ${response.statusText}`;
+        try {
+          // Get response body as text first
+          const errorText = await response.text();
+          console.log(errorText);
+
+          // Try to parse as JSON
+          try {
+            const errorBody = JSON.parse(errorText);
+            errorMessage = errorBody.message || JSON.stringify(errorBody);
+          } catch {
+            // Not JSON, use plain text
+            errorMessage = errorText || errorMessage;
+          }
+        } catch {
+          // Couldn't read body at all
+        }
+        throw new Error(`could not send email: ${errorMessage}`);
       }
     } else {
       console.log(