@Pstork1
I am having the same issue except I'm writing to SharePoint not OneDrive.

Full error output
"statusCode": 400,
"headers": {
"Pragma": "no-cache",
"x-ms-request-id": "2087199d-855e-4500-a64f-00d70371e9e8",
"Strict-Transport-Security": "max-age=31536000; includeSubDomains",
"X-Content-Type-Options": "nosniff",
"X-Frame-Options": "DENY",
"Cache-Control": "no-store, no-cache",
"Set-Cookie": "ARRAffinity=44681089155cffee5d6ea46eb43a0a3c4b551bd2ba6e6eff95774f120dc70b73;Path=/;HttpOnly;Secure;Domain=wordonlinebusiness-wus.azconn-wus-01.p.azurewebsites.net,ARRAffinitySameSite=44681089155cffee5d6ea46eb43a0a3c4b551bd2ba6e6eff95774f120dc70b73;Path=/;HttpOnly;SameSite=None;Secure;Domain=wordonlinebusiness-wus.azconn-wus-01.p.azurewebsites.net",
"Timing-Allow-Origin": "*",
"x-ms-apihub-cached-response": "false",
"x-ms-apihub-obo": "true",
"Date": "Tue, 22 Mar 2022 16:53:28 GMT",
"Content-Length": "386",
"Content-Type": "application/json",
"Expires": "-1"
},
"body": {
"status": 400,
"message": "Unsupported Word Document version. Please select a document edited on Word 2010 or newer.\r\nclientRequestId: <<removed>>",
"error": {
"message": "Unsupported Word Document version. Please select a document edited on Word 2010 or newer."
},
"source": "wordonlinebusiness-wus.azconn-wus-01.p.azurewebsites.net"
}
I am using a definitely using a .docx file.

And the most current version of WORD:
