Hi JZama110492 , if you open the sales file in a text editor, you'll see that amounts over $1000 have quotes around them, as do any fields with commas in them. I assume you are editing the file in Excel before saving it as a text file, tab-delimited.
You need to remove the quotes from the file before importing it.
You could format all the amounts as general, then search the file in Excel for commas and replace with nothing (to delete them. Then save and import.
Try a test file with 10 invoices in it first. Then if that works, import all the rest as one file.