Hit the Reconnect button if you see 'QuickBooks Error 103' beneath the error message. Hand-enter the username and password with caution. Then hit the Update Sign-in Info icon. Check the connectivity of your bank. Go over to the Self Service Section and then Security Center. Otherwise, choose Manage Security from the drop-down box under Business Tools. Furthermore, Third-Party Access should be avoided.
https://www.quickbak.com/quickbooks-error-103/