Add overlay video and animated text (textbox and shadow) with FFmpeg I'm trying to figure out how this works, but I couldn't find the final solution.

ffmpeg -i input -i overlayvideo \
-filter_complex \
"[0:v] setpts=PTS-STARTPTS [v01]; \
[1:v] setpts=PTS-STARTPTS [gradient]; \
[2:v] drawtext=fontfile=...font.ttf: text='Test': fontcolor=white:fontsize=54: shadowcolor=black@0.6:shadowx=4:shadowy=2: \
box=1: boxcolor=a60000@0.4:boxborderw=10:x='310':y='350',format=yuva444p,fade=t=in:st=1:d=1:alpha=1,fade=t=out:st=7:d=1:alpha=1, setpts=PTS-STARTPTS[v1][txt]; \
[v01][gradient] overlay [v02]; \
[v02][txt] overlay=[outv]" \
-c:v libx264 -profile:v main -level:v 3.1 -pix_fmt yuv420p -c:a aac -map [outv] \
-f mp4 -y 'output.mp4'


The error message:
No output pad can be associated to link label 'txt'.
Error initializing complex filters.
Invalid argument*



I've studied these solutions, but for the time being, I don't understand where I made the mistake.

https://stackoverflow.com/questions/47322739/ffmpeg-overlay-multiple-fading-texts-with-different-colors



https://trac.ffmpeg.org/wiki/Create%20a%20mosaic%20out%20of%20several%20input%20videos



What have I forgotten why the output is not good?
Thank you for your advice and help.
You only have two inputs, so 2:v can't exist. Instead, you'll need a base canvas to draw the text upon. I've used the color source filter for that. And you probably want that canvas to be the same size as the video. I've used scale2ref for that. 

ffmpeg -i input -i overlayvideo \
-filter_complex \
"[0:v] setpts=PTS-STARTPTS [v01]; \
[1:v] setpts=PTS-STARTPTS [gradient]; \
color=black@0:duration=8,format=yuva444p[txtbase];[txtbase][v01]scale2ref[txtbase][v01];[txtbase] drawtext=fontfile=...font.ttf: text='Test': fontcolor=white:fontsize=54: shadowcolor=black@0.6:shadowx=4:shadowy=2: \
box=1: boxcolor=a60000@0.4:boxborderw=10:x='310':y='350',fade=t=in:st=1:d=1:alpha=1,fade=t=out:st=7:d=1:alpha=1[txt]; \
[v01][gradient] overlay [v02]; \
[v02][txt] overlay[outv]" \
-c:v libx264 -profile:v main -level:v 3.1 -pix_fmt yuv420p -c:a aac -map [outv] \
-f mp4 -y 'output.mp4'