I don’t do RDS, but I add metadata to my stream so that the track/artist shows on my stream receiver. My playout software writes it to a file, so I include the entire path to the file (in my case C:\AHK Scripts\MetaData.txt) and BA1 picks the name up from there.
Going by the pop-up, it appears to be looking for a file location because my stream box says “/hd1/strm/read_md_file_name” in the corner, similar to the parameter yours is displaying.