Apply suggestions from code review

Co-authored-by: ldecarvalho-doc <[email protected]>

Author: jsudraud

pages/billing/troubleshooting/fix-common-billing-issues.mdx

@@ -23,15 +23,15 @@ Your payment may have failed due to insufficient funds, an issue with your payme
  - Ensure you have enough funds in your bank account. 
  - If payment still does not work, the reason for the failure is indicated in the error message in the console
 <Message type="tip">
-  A "card_declined" error message means the payment was refused by your bank. Contact your bank for more details.
+  A `card_declined` error message means the payment was refused by your bank. Contact your bank for more details.
 </Message>
 
 **If you are paying via SEPA direct debit, try the following:**
 - Verify that your SEPA mandate is correctly set up to ensure future payments are processed.
 - Verify that your billing address matches the country of your bank account.
 - Retry the payment.
 <Message type="requirement">
-  Any unpaid invoice must be paid by credit card.
+  Unpaid invoices must be paid by credit card.
 </Message>
 
 ## I did not receive my invoice