GIF shows the fallback, not the name

Check, in order

1. Is the recipient in the batch? New sign-ups after the upload get the fallback until you run a batch for them.
2. Does the merge token produce the same value as the identifier column? The file name is the identifier: if you uploaded user_id and the email substitutes email, nothing matches.
3. Case and characters. If you ticked lowercase on upload, the token's value must be lower-case too (most tools have a | downcase filter). Spaces and punctuation are normalised identically on both sides; non-Latin identifiers become stable hash slugs, so use an ASCII id column where you can.
4. Did the row fail? Failed rows are listed in the batch's failed-rows CSV with the reason.
5. Is the batch complete? Rows still rendering resolve to the fallback until they land.

Test it directly

Open the dynamic URL in a browser with a real identifier typed into the file name. If that shows the fallback, the problem is on our side of the equals sign; if it shows the name, it is the merge token.