First, nothing was damaged. An import creates drafts, never live listings, so a bad upload has not put anything on sale and has not changed your existing items — unless a row carried an id, which updates that listing deliberately.
The app shows you what it read, row by row, with the problem named. Start there rather than guessing.
The usual six
1. A missing title or price. Those two are the only required columns. A row without either cannot become a listing.
2. More than 200 rows. Split the file and upload it twice.
3. Photo links that are not web addresses. They must be addresses beginning with http. A path from your own computer, a Google Drive share link that needs sign-in, or a filename will not fetch.
4. Too many photo links in one row. Capped at the same number a listing allows; the extras are ignored rather than failing the row.
5. A price that is not a number. Currency symbols, spaces and commas inside the figure are the usual culprits. Also check your spreadsheet has not turned a price into a date, which it does more often than you would think.
6. The header row renamed. The columns are matched by name.
The one that is not an error
A row with no photograph still imports. It stays a draft until you add a picture — that is the design, not a failure.
If you meant to update and it created copies
You left out the id column. The id is how a row says "change this listing" rather than "make a new one", and it is written by the inventory export for exactly this.
Delete the duplicates, export again, edit that file, and upload it back. Listing a lot of items quickly
If the file will not upload at all
Save it as CSV, plain, from your spreadsheet program.
Check the first row is the header, not a title or a blank line.
Remove merged cells and formulas — export values, not formulas.
Before you upload a big one
Try five rows first. Five rows tells you whether your columns, your photo links and your price formatting are right, and costs a minute. Two hundred rows with the same mistake costs an evening.
If the problem named is one you do not understand
Raise it under Listings & inventory, which exists for adding items, stock and taken-down items — with the row and what it said. How to raise an issue
More: listing a lot of items quickly, my listing is not showing up, weights and dimensions.