When manually typing in check number and select save, why does it default back to a different check number?

You're right, Tiffany. When you manually enter a check number, QuickBooks Online (QBO) should save without altering it. 

In your case, both users are using the same account, causing the check number to revert.

When two users are managing checks on the same account, QBO tracks the check numbering in sequence for the entire account, not per user. As a result, if one person enters a check number and saves it, the shared sequence could overwrite or adjust the number based on the last check saved by the other user. Thus, the manually entered check number doesn't always remain the same.

To avoid conflicts, we recommend assigning different check number ranges for each user. For example, CA can use the check numbers 1-10, and IA can use the numbers 11-20. This way, each user works within their own range, and the numbering system doesn’t interfere between users.

It's also a good idea to coordinate who is working on checks at any given time. Avoid working on checks simultaneously to reduce any risk of overwriting each other’s check numbers.

Additionally, when you select Print Check after entering details of your check, it will not have a check number on it. This is because the program adds it to the print queue, and the check number is finalized only after it’s printed. Ensure to review the check sequence regularly and adjust manually as needed before printing if necessary.

See this article for additional info: Print a check in QuickBooks Online.

You can also set your QuickBooks settings to warn you if a duplicate check number is used. You can do so by following the steps below: 

1. Go to the Gear icon and select Account and Settings.
2. From the Advanced tab, look for Other preferences, then click the Edit button.
3. Toggle the sign "Warn if duplicated check number is used".
4. Click Save, then Done.

By implementing these measures, you can prevent conflicts with check numbering and streamline the workflow for both users.

Please don’t hesitate to reach out if you have additional questions or need further assistance. We'd be glad to provide additional help.