I'm here to assist you in resolving the issue of downloading missing transactions from your Capital One credit card into QuickBooks Online, Samantha. 

You can try to refresh the connection between QuickBooks Online and your Capital One account. This often prompts QuickBooks to pull up any available transactions from your bank. 

Here's how you can do it:

1. Go to Transactions and select Bank transactions. 
2. Click on Update. 
3. Follow the prompts to refresh your account. 

If that doesn't work, you may need to manually import the missing transactions into QuickBooks Online. You can do this by downloading a transaction file from your Capital One account and then importing it into your account. Ensure that the file format is compatible with QuickBooks Online (such as CSV or QBO).

Download bank transactions:

1. Go to your online banking account to get your file.
2. Check or follow your bank’s instructions to get a copy of the data and then save it on your computer.
3. Ensure that the data range is at least one day before your oldest transaction to avoid duplicates.
4. Please take note of the supported file format and size. It should be either a Comma-Separated Values (CSV) or a QuickBooks Online (QBO) file.
5. Download your transactions and save the file to your desktop.

To upload the file to your QuickBooks account: 

1. From the Bank transactions page, click the Link account drop-down and select Upload from file.
2. On the window that appears, click the Browse button or Select files and choose the file that you’ll be downloading.
3. Follow the onscreen instructions to finish uploading the transactions. 

Here's more information about adding your transactions manually in QuickBooks Online (QBO): Manually upload transactions into QuickBooks Online.

After importing your transactions, make sure to categorize and match them to ensure accuracy and avoid duplicates. You can also reconcile your account to keep your books up to date: 

• Categorize and match online bank transactions in QuickBooks Online
• Reconcile an account in QuickBooks Online

That should help you get your missing transaction. If you have any further questions or need additional assistance, feel free to reply here. I'm here to help! Have a wonderful day ahead!