Https POST request. 200 in postman 400 in code

Question

I tried to call an endpoint.

• Requests called via Postman ended fine.
• Requests called via Axios or node-fetch library were all ending with 400.

Firstly I tried to match my headers 1:1 with Postman... then, my idea was to compare these requests in Fiddler. Unfortunately, I was able to see there only requests from postman.

• Why I can't see my 400 requests in fiddler? (maybe I am missing some settings there)
• What can potentionaly cause this 400 - Bad request issue? (or any tips for investigation)

Example fake request.

const emailRequest: EmailRequest = {
  replyTo: 'test',
  subject: 'test',
  text: 'test',
};

fetch('https://someaddress.com/sendemail',
        {
          method: 'post',
          headers: {
            'Content-Type': 'application/json',
            'Cache-Control': 'no-cache, no-store, max-age=0, must-revalidate',
            Date: 'Tue, 19 Apr 2022 04:59:50 GMT',
            server: 'Apache', 
            'x-content-type-options': 'nosniff',            
            'X-Correlation-Id': 'b2d3808a-a9da-49a2-97eb-e3a222624062',
            'x-frame-options': 'DENY', 
            'x-xss-protection': '1; mode=block', //check
            Authorization:
              'Bearer (my bearer)',            
          },
          body: JSON.stringify(emailRequest),          
        },
      )

Thank you very much for your time and ideas.