Thanks for bringing this matter to our attention, @SunlitFunlit. I know how important it is to pay your obligations to your vendors via ACH transaction on time. With this, let me share why some of your payments got declined and guide you on the steps you need to take to help resolve the issue.

For the time being, based on our records, there aren't any reported cases of declined vendor payments in QuickBooks Online (QBO). Your last two invoice payments may have been declined due to any of the following:

• Insufficient fund
• Account frozen
• Policies or regulations prohibited or ACH limit has been reach
• The account number doesn't match the individual on the payment
• The payment refused by their bank

When a vendor (ACH) payment is declined, you'll receive a notification via email. It'll provide you with specific info or the cause of why your payments are declined and guide you on how you can resolve them.

Alternatively, you can use a different method to pay your vendor invoices. However, if none of them works, I encourage you to contact our Customer Care team. They can create a case to further investigate the issue and guide you with a fix. Here's how:

1. Sign in to your QBO company.
2. Go to the Help (?) menu.
3. Select the Search tab.
4. Click the Contact Us button.
5. Enter a brief description of your concern in the What can we help you with? field.
6. Select Continue.
7. Choose a way to connect with us (Send a message or Get a callback).

Also, you may want to check out one of our Help pages as your reference to further guide you in managing your vendors, paying expenses and bills, and inventories in QBO: Expenses and Vendors Help Articles. 

Please let me know in the comments if you have other concerns about paying vendor invoices and managing expenses in QBO. I'll gladly help. Take care always, @SunlitFunlit.