IFS Open & Append

I'm trying to open a stream file to append data to it. This is the code I
grabbed from the internet to test:

fd = open(%trim($file_name)
: O_WRONLY+O_CREAT+O_APPEND+O_CCSID
: S_IRGRP + S_IWGRP + S_IXGRP:819);
callp close(fd);
fd = open(%trim($file_Name):O_WRONLY+O_TEXTDATA);

$xml = '<Items>';
callp write(fd: %addr($xml): %len(%trim($xml)));

when I write to the stream file it goes to the beginning of the file.

I tried reading through the file using this first, then using write but it
did the same thing

dow (read(fd: %addr(Buf): %size(Buf)) > 0);
buf = *allx'20';
enddo;

How can I add to the end of a stream file?