The usual cause is junk characters in the Message column. Rows containing them fail, and that normally happens when content is pasted from Word or another rich text editor, which carries invisible characters across.

Type the message directly, or paste as plain text, then re-upload.

To see exactly which rows failed, open the File Uploads Summary report. Comparing the uploaded count against the processed count tells you how many rows did not go through.

Other things to rule out: missing country codes, an unrecognised header row, and a DLT template mismatch on India traffic.