If you discover one of your categories is missing, or the category dropdown box has disappeared from any of your cells in the Category column in the Transactions sheet. We include steps for how to fix this issue and tips for how to avoid it in the future.
Review the location of your Category column in the Transactions sheet and Categories sheet. What column letter does the Category column correspond to in both sheets? Usually in Transactions it's column D and in Categories it's column A. You'll need to adjust the range references below to reflect the location of your Category column.
In your Transactions sheet, select the Category column starting with row 2 and drag down the column to select the rest of the cells in the column. (Don't select the top row "Category" header cell.)
Open the Data Menu
Choose Data Validation...
Configure the cell range. If your Category column is in column D (most cases) "Transactions!D2:D" (without the quotes). Using D2:D, instead of D2:D355 (or some other row number) will ensure that all new rows added get the validation too.
Set the criteria. This will always be "List from a range" and in most cases will be "Categories!A2:A" (without the quotes).
How to Avoid this Issue
Add new categories to the bottom of the Categories list instead of inserting new rows.
If you're pasting manually added transactions into your Transactions sheet, right click and choose Paste Special > Paste Values Only to ensure the data validation gets added to new rows.