The issue with Song Select is that they only make their chord charts available in PDF format. The PDF files they create are more like pictures of a chart and don't contain any text. This means that OnSong has to submit the file to an OCR server (optical character recognition) to have a computer "read" the file. Even so, a PDF file does not contain information that is useful for aligning chords over lyrics accurately which means adjustments are required.
Many people have a Song Select account which is why we continue to support it, but I would recommend a service like Rockin' With The Cross or WorshipReady.com instead. These charts are created for OnSong in text-based chord charts that work out of the box.