Couldn't recognize fields from Base64

Hi all,

I am trying to upload a document with valid form fields to a new envelope, but getEnvelopeDocGenFormFields can't recognize any fields from Base64. code. I am sure that the form of the document(docx) is valid.

byte[] fileBytes = Files.readAllBytes(Paths.get("/Users/.../Document_Template.docx"));

Document document = new Document();

document.setDocumentBase64(Base64.getEncoder().encodeToString(fileBytes));

document.setName("SampleDocument.docx");

document.setFileExtension("docx");

document.setDocumentId("1");

ArrayList<Document> documents = new ArrayList<>();

documents.add(document);

envelopeDefinition.setDocuments(documents);

final EnvelopeSummary envelopeSummary = envelopesApi.createEnvelope(accountId, envelopeDefinition);

final String envelopeId = envelopeSummary.getEnvelopeId();

// Step 3 - Get Fields from document that need to be merged with custom data

final DocGenFormFieldResponse formFieldResponse =
envelopesApi.getEnvelopeDocGenFormFields(accountId, envelopeId);

result:

formFieldResponse.docGenFormFields == null