Yes, Kimc3. QuickBooks allows you to link multiple financial institutions. There are a few things to check if you're having trouble connecting your client's accounts.
To begin, could you please describe what happens when connecting the second account? Did you receive any prompt messages? Also, which bank are you attempting to link with? This information will help us determine any topics reported on our end.
In the meantime, I suggest checking your bank’s website for maintenance updates that might affect the connection process. If none, I recommend troubleshooting with an incognito browser or another QuickBooks-supported website to rule out any browser-related issues.
Also, note that you only need to connect the parent account to download transactions if the second account is a subaccount of the first. Linking the second one separately isn't necessary.
This thread will remain open if you have any additional banking concerns.