Troubleshooting
Most import problems have one of three causes. The Power-Up is not added to that board, so no button appears. The browser blocked the sign in pop-up. Or members cannot be attached because Trello only allows assigning people already on the board. Failed rows download as a small file so you can fix and re-import only those.
There is no Import button on the board
The Power-Up is not added to that board. Board menu, then Power-Ups, then the Custom tab, then add it. If it is not listed there, the board belongs to a different Workspace from the one the Power-Up was registered under.
Connecting to Trello fails, or the window closes instantly
Two usual causes. Your browser blocked the pop-up, so allow pop-ups for trello.com. Or the address the Power-Up is served from is not listed as an allowed origin on its API key, which is a setup problem rather than something you can fix from the board.
It says the API key is missing
The copy of the Power-Up being loaded has no key configured. If you host it yourself, that is config.js, and the deployed copy is older than the edit.
Members are not being attached
Trello only allows assigning people who already belong to the board. Names that match nobody are listed in the preview before the import runs, and their cards are still created without them. Add the people to the board, then import again.
Dates are a day out, or in the wrong month
3/9/2026 is genuinely ambiguous. Tick Dates are day first for 31/12/2026 style dates.
A date with no time is deliberately set to midday so it cannot slip to the previous day for someone in another timezone. If a date looks a day out in a different way, check whether the spreadsheet cell is text or a real date.
Nothing was created and it said preview
The window was opened outside Trello without signing in. A yellow banner at the top says so before you start. Open the board and use the Import button there, or sign in from the window itself and pick a board.
Some rows failed
Click Download failed rows. You get a small file with the row number, the card title and the error for each one. Fix those, then import that small file rather than the original, because re-importing the whole file would duplicate every card that already worked.
The import slows down near the end
Trello rate limits how fast an application may write. The importer stays under the limit deliberately and backs off when Trello asks it to, so a long import keeps going rather than failing. A few hundred cards takes a couple of minutes.
I imported the same file twice
There is no duplicate detection and no undo. Select the duplicated cards on the board and archive them, or archive the whole list if it was a fresh import.
A file will not open at all
See supported file formats. The most common case is the old binary .xls, which needs saving as .xlsx or .csv first.