invalid byte sequence for encoding "UTF8"

psql=# copy tmp from '/path/to/file.csv' with delimiter ',' csv header encoding 'windows-1251';

Adding encoding option worked in my case.

If you need to store UTF8 data in your database, you need a database that accepts UTF8. You can check the encoding of your database in pgAdmin. Just right-click the database, and select "Properties".

But that error seems to be telling you there's some invalid UTF8 data in your source file. That means that the copy utility has detected or guessed that you're feeding it a UTF8 file.

If you're running under some variant of Unix, you can check the encoding (more or less) with the file utility.

$ file yourfilename
yourfilename: UTF-8 Unicode English text

(I think that will work on Macs in the terminal, too.) Not sure how to do that under Windows.

If you use that same utility on a file that came from Windows systems (that is, a file that's not encoded in UTF8), it will probably show something like this:

$ file yourfilename
yourfilename: ASCII text, with CRLF line terminators

If things stay weird, you might try to convert your input data to a known encoding, to change your client's encoding, or both. (We're really stretching the limits of my knowledge about encodings.)

You can use the iconv utility to change encoding of the input data.

iconv -f original_charset -t utf-8 originalfile > newfile

You can change psql (the client) encoding following the instructions on Character Set Support. On that page, search for the phrase "To enable automatic character set conversion".