Setting Reply-to in mailgun - mailgun

Question

I've seen the API for this which suggests adding the Reply-To header or h:Reply-To param. I don't have any experience with headers so that may be why I'm having trouble with this.
I'm trying to construct the request in postman, and I've tried putting Reply-To as a header key and an email as the value, and I've also tried without that header and instead with a param with the key h:Reply-To but when I hit "reply" to the email that gets sent, it always replies to the sender instead of my reply-to address.
Can anyone help me?
as header
POST /v3/sandboxXXXXba.mailgun.org/messages?from=messages#xxxx.com& to=xxxx1#gmail.com& subject=hello& text=mailgun-test HTTP/1.1
Host: api.mailgun.net
Reply-To: xxxx2#gmail.com
Authorization: Basic xxxx
cache-control: no-cache
Postman-Token: xxxxx
as param
POST https://api.mailgun.net/v3/sandboxXXXX.mailgun.org/messages?from=messages#domain.com&to=me#gmail.com&subject=hello&text=mailgun-test&h:Reply-To=me#gmail.com
aka:
POST /v3/sandboxXXXXX33ba.mailgun.org/messages?from=messages#mydomain.com& to=myaddress#gmail.com& subject=hello& text=mailgun-test& h:Reply-To=myaddress#gmail.com HTTP/1.1
Host: api.mailgun.net
Authorization: Basic xxxxx
User-Agent: PostmanRuntime/7.15.2
Accept: */*
Cache-Control: no-cache
Postman-Token: xxxx
Host: api.mailgun.net
Accept-Encoding: gzip, deflate
Content-Length:
Connection: keep-alive
cache-control: no-cache

Answer 1

So it should be a form-data body parameter:
POST /v3/skedda.co/messages HTTP/1.1
Host: api.mailgun.net
Authorization: Basic YX...
User-Agent: PostmanRuntime/7.15.2
Accept: */*
Cache-Control: no-cache
Postman-Token: ...
Host: api.mailgun.net
Accept-Encoding: gzip, deflate
Content-Type: multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW
Content-Length: 781
Connection: keep-alive
cache-control: no-cache
Content-Disposition: form-data; name="from"
postmaster#...com
------WebKitFormBoundary7MA4YWxkTrZu0gW--,
Content-Disposition: form-data; name="to"
a....com
------WebKitFormBoundary7MA4YWxkTrZu0gW--,
Content-Disposition: form-data; name="subject"
link test
------WebKitFormBoundary7MA4YWxkTrZu0gW--,
Content-Disposition: form-data; name="html"
<h1>Hello world</h1>
------WebKitFormBoundary7MA4YWxkTrZu0gW--,
Content-Disposition: form-data; name="h:Reply-To"
notifications#...com
------WebKitFormBoundary7MA4YWxkTrZu0gW--
or in Postman itself