When you import a csv file into HubSpot, you can download a list of any errors that occurred during the import by navigating to Contacts > Imports > errors.
On that import file, you'll find a column that explains the error "reason". You may find that one of your errors reads, "Header and row sizes don't match"
- That error means that you have information in some columns where there is no header indicating the field where those values should be stored
- This can happen if your csv file once had additional columns containing information that were not deleted properly before importing the file
- If you are opening the csv file in a spreadsheet editor (such as Excel) the extra columns may look blank, but if you open the file in a text editor (such as notepad), you should see a number of superfluous commas
- To correct this, you can do a find (clt + f) and replace all of those commas with one comma, then re-save and re-import your csv file