%CSP.Page - proper way to change ContentType to display text error or return expected pdf content

I want to create a CSP page that returns a pdf.
The pdf is identified by a pdftoken parameter.

My goal is to validate the token and return the pdf (ContentType=”application/pdf”) if the token
is good and return a text error message "Bad Token" (ContentType=”text/plain”) if the token is missing or bad.

My issue seems to be associated with ContentType. I can define one ContentType that works for the pdf or the error message.
I am unable to change the ContentType.

Any assistance is appreciated.

ClassMethod OnPage() As %Status
{
set pdfToken=$get(%request.Data("pdfToken",1))
if pdfToken="" {
set PDFError("ErrorCode")=400
set PDFError("ErrorText")="missing pdftoken"
set %response.ContentType="text/plain"
set %response.Status =”400 Bad Request”
quit %response.Status
}

//token passed – serve the pdf
set %response.ContentType="application/pdf"
set PDFFileName=$piece(^TokenData(pdfToken),"^",1)
set stream=##class(%FileBinaryStream).%New()
do stream.LinkToFile(PDFFileName)
do stream.OutputToDevice()
quit $$$OK
}