OpenTopoMap: Show elevation profile underneath GPX

Dear all,

I have digitized a line and imported it into the OpenTopoMap GUI ( with the GPX button. The line appears but there is no elevaiton information shown in the displayed chart. The chart displays a line when I move my mouse over the line, but it does not display any information data (NaN m).
I have tested different browsers (Firefox, Chrome) and line formats (gpx, kml, geojson).
Does anyone have an idea what might be wrong here?

Happy about any comment

Maybe an obvious question, but does your gpx file contain elevation data?

Thank you for the reply, sometimes the obvious is the most important… I thought the heights would be extracted from the OpenTopoMap data below the map (SRTM). Accordingly, my gpx did not have tags inside.
I consider this answered, thank you again.