Use
ffmpeg -f lavfi -i color=c=black:s=360x360 -i audiofile -vf drawtext="fontfile='/usr/share/fonts/truetype/freefont/FreeSerifBold.ttf': \ text='Testing VPS Live Stream': fontcolor=white: fontsize=20: box=1: boxcolor=black: \ x=(w-text_w)/2: y=(h-text_h-line_h)/2,realtime" -af arealtime -c:v libx264 -preset veryfast -maxrate 100k -bufsize 300k -f flv rtmp://streamurl/live/mykey