The correct way of calling a SAML http request from Angular/JavaScript

Question

I have been making an http request to a SAML endpoint

public testSAML(token) {
const headers = new HttpHeaders({
    'Content-Type': 'application/x-www-form-urlencoded',
    'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9',
});

const options = {
  headers
};
const reqBody = new HttpParams()
.set("SAMLRequest", token); 

this.httpClient.post('https://example.com/oamfed/idp/samlv20', reqBody, options)
  .subscribe(
    (response:any) => {
      console.log(response)
    },
    (error:any) => {
      console.log(error)
    }
  );}

The first thing this is directly going to the error page. If I try the same request from the SOAP UI I am getting the expected response