SharePoint REST API - update metadata Document Library Item when value string includes apostrophe (single quote) character

I want to update a metadata column for an item (document set) in a SharePoint document library using REST API (via VBA).

The below (vba) code extract/simplification works fine for simple cases, for example when szQuestionText = "My Simple Question"

However, it fails for cases when szQuestionText includes special characters - the one I'm presently tripping over is an apostrophe (single quote), however, I expect there would be other cases too.

e.g. when szQuestionText = "Where's Wally" the below code would fail. Note that the troublesome string ends up in the body of the HTTP POST message, not in the URL, per se (if that makes any difference to the solution).

Various research led me to try 'escaping' the apostrophe in various ways, however if it updated the column's value field at all, then the entire 'escape sequence' found its way into the column's value field - not an acceptable outcome.

e.g.

szQuestionText = "Where%27s Wally"
szQuestionText = "Where%27%27s Wally"
szQuestionText = "Where%27%27s+Wally"

What changes are required to handle this situation? szQuestionText = "Where's Wally"

szDigest = "" 'assume populated at runtime with actual/valid value
szURL = "https://myprojectname.sharepoint.com/mysites/subsiteL1/subsiteL2/subsiteL3/_api/web/lists/getbytitle('MyQuestions')/items(25)"
szBody = "{ '__metadata': { 'type': 'SP.Data.MyQuestionsItem' }, 'QuestionText': '" & szQuestionText & "' }"
With oHttp
    .Open "POST", szURL, False
    .setRequestHeader "accept", "application/atom+xml"
    .setRequestHeader "X-HTTP-Method", "MERGE"
    .setRequestHeader "IF-MATCH", "*"
    .setRequestHeader "Content-Type", "application/json;odata=verbose"
    .setRequestHeader "X-RequestDigest", szDigest
    .setRequestHeader "Content-Length", Len(szBody)
    On Error Resume Next
    .Send szBody
end with

Kind regards,

John.