Failure to enable imageless mode for Document AI form parser

[oregonoutpt]

I am passing a PDF to the form parser processor (most recent stable release) in an apps script.  No matter what I do, I cannot seem to enable the imageless option to permit synchronous processing of PDFs of length 16-30 pages.  I get a server error 500 with the message:

"This processor version only supports up to 15 pages per document shard. If using the UI or sync pre..."

Below is my code.  I am a novice at this, so it is entirely possible that I have a fundamental misunderstanding of how this should work.

function callDocumentAI(file, imageless = false) {

const token = ScriptApp.getOAuthToken();

const url = `https://${PROJECT_LOCATION}-documentai.googleapis.com/v1/projects/${PROJECT_ID}` +

`/locations/${PROJECT_LOCATION}/processors/${FORM_PARSER_PROCESSOR_ID}:process`;

const inlineDoc = {

content: Utilities.base64Encode(file.getBlob().getBytes()),

mimeType: 'application/pdf'

};

// Build request body

const body = { inlineDocument: inlineDoc };

if (imageless) {

// Enable imageless mode flag

body.imageless_mode = true;

}

// Prepare HTTP options

const options = {

method: 'post',

contentType: 'application/json',

headers: { Authorization: `Bearer ${token}` },

payload: JSON.stringify(body)

};

const resp = UrlFetchApp.fetch(url, options);

return JSON.parse(resp.getContentText());

}

Thank you in advance for any insight you might have.