Auth failure: DROPBOX: (400) missing required field ‘grant_type’

DROPBOX: (400) Bad input parameter. Response from server: {"error": "unsupported_grant_type", "error_description": "missing required field \"grant_type\""}

is the response on network admin panel > BackWPup > tab ‘To: Dropbox’ after ‘Get Dropbox App auth code’ and pasting that code into the form field, and then clicking ‘Save changes’

Debug Info follows:

WordPress version: 6.1.1
BackWPup version: 4.0.0
PHP version: 8.0.0 (32bit)
MySQL version: 10.3.27-MariaDB
cURL version: 7.73.0
cURL SSL version: OpenSSL/1.1.1h
WP-Cron url: https://www.<domain>.com/wp-cron.php
Server self connect: Response Test O.K.
Document root: C:\Users\User\Documents\Inetpub\domains\4assistance.com\public_html
Temp folder: C:/Users/User/Documents/Inetpub/domains/4assistance.com/public_html/wp/wp-content/temp/backwpup-a58db4/
Log folder: C:\Users\User\Documents\Inetpub\domains\4assistance.com\public_html\wp\wp-content\uploads\backwpup-a58db4-logs/
Server: Microsoft-IIS/7.5
Operating System: WINNT
PHP SAPI: cgi-fcgi
Current PHP user: 4assPool
Maximum execution time: 600 seconds
BackWPup maximum script execution time: 30 seconds
Alternative WP Cron: Off
Disabled WP Cron: Off
CHMOD Dir: 0755
Server Time: 18:56
Blog Time: 11:56
Blog Timezone: America/Chihuahua
Blog Time offset: -7 hours
Blog language: en-US
MySQL Client encoding: utf8
PHP Memory limit: 256M
WP memory limit: 64M
WP maximum memory limit: 256M
Memory in use: 4.00 MB
Disabled PHP Functions:: system, shell_exec, passthru, mysql_list_dbs, ini_alter, dl, symlink, link, chgrp, leak, popen, apache_child_terminate, virtual, mb_send_mail
Loaded PHP Extensions:: Core, PDO, Phar, Reflection, SPL, SimpleXML, Zend OPcache, bcmath, bz2, calendar, cgi-fcgi, ctype, curl, date, dom, exif, fileinfo, filter, gd, hash, iconv, imagick, intl, json, libxml, mbstring, mysqli, mysqlnd, openssl, pcre, pdo_mysql, readline, session, standard, tokenizer, xml, xmlreader, xmlwriter, zip, zlib

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