RestSharp latest version breaks my API's post method (add Guid before and after the body) - nuget

Question

Since latest version of RestSharp, all my post API's are failing because something has been added to the bodies I send.
Looks like a Guid id is generated and is added before and after the body for each call; the issue is it's not accepted by all my API's providers.
FYI, I created 2 identical console apps, one with version "106.12.0", and one with latest version "107.3.0". please see below the result:
Thanks in advance to help me with this
BR
-Vince
Examples:
Working with Version="106.12.0" :
before:
Content-Type: text/plain; charset=utf-8
Content-Disposition: form-data; name="application/xml"
<SMSBoxXMLRequest>
<username>cnoxxxx</username>
<!-- password hidden -->
<command>WEBSEND</command>
<parameters>
<service>VALAIS</service>
<text>Test de Message Sms 1</text>
<test></test>
<receiver>[phone]</receiver>
</parameters>
</SMSBoxXMLRequest>
after:
Not Working with Version="107.3.0" :
**--497993c6-3ef7-47fb-b527-403c1eefedf8**
Content-Type: text/plain; charset=utf-8
Content-Disposition: form-data; name="application/xml"
<SMSBoxXMLRequest>
<username>cnoxxxx</username>
<!-- password hidden -->
<command>WEBSEND</command>
<parameters>
<service>VALAIS</service>
<text>Test de Message Sms 1</text>
<test></test>
<receiver>[phone]</receiver>
</parameters>
</SMSBoxXMLRequest>
**--497993c6-3ef7-47fb-b527-403c1eefedf8--**
**--3277a8db-bd83-4f3c-af2e-d34efe76fe98**
Content-Type: text/plain; charset=utf-8
Content-Disposition: form-data; name="application/xml"
<SMSBoxXMLRequest>
<username>cnoxxxx</username>
<!-- password hidden -->
<command>WEBSEND</command>
<parameters>
<service>VALAIS</service>
<text>Test de Message Sms 2</text>
<test></test>
<receiver>[phone]</receiver>
</parameters>
</SMSBoxXMLRequest>
**--3277a8db-bd83-4f3c-af2e-d34efe76fe98--**
**--5b81fa95-a0b9-4f5c-9242-742734b0241e**
Content-Type: text/plain; charset=utf-8
Content-Disposition: form-data; name="application/xml"
<SMSBoxXMLRequest>
<username>cnoxxxx</username>
<!-- password hidden -->
<command>WEBSEND</command>
<parameters>
<service>VALAIS</service>
<text>Test de Message Sms 3</text>
<test></test>
<receiver>[phone]</receiver>
</parameters>
</SMSBoxXMLRequest>
**--5b81fa95-a0b9-4f5c-9242-742734b0241e-**-