ATS. Thx.
sample code (doesn't work even if converted to string):
tSPXData = FinancialData["^SPX","2021201"]["Path"];
trace := <|
"X" -> DateString[#, "ISODate"]&/@tSPXData[[;;,1]],
"y" -> tSPXData[[;;,2]],
"type" -> "scatter",
"mode" -> "lines"
|>
Plotly[trace]