【CORS】クロスドメインによるエラーを解決したい

前提・実現したいこと

WordPressを使って記事を配信しています
あるドメインでは配信出来るのですが別のドメインにするとクロスドメインエラーが出ます。
それを解決したい。

発生している問題・エラーメッセージ

Access to XMLHttpRequest at 'https://dev.〇〇.com/wp-admin/admin-ajax.php' from origin 'http://localhost:8100' has been blocked by CORS policy: The 'Access-Control-Allow-Origin' header contains multiple values '*, *', but only one is allowed.

core.js:6185 ERROR Error: Uncaught (in promise): HttpErrorResponse: {"headers":{"normalizedNames":{},"lazyUpdate":null,"headers":{}},"status":0,"statusText":"Unknown Error","url":"https://dev.〇〇.com/wp-admin/admin-ajax.php","ok":false,"name":"HttpErrorResponse","message":"Http failure response for https://dev.〇〇.com/wp-admin/admin-ajax.php: 0 Unknown Error","error":{"isTrusted":true}}
    at resolvePromise (zone-evergreen.js:798)
    at zone-evergreen.js:705
    at rejected (tslib.es6.js:72)
    at ZoneDelegate.invoke (zone-evergreen.js:364)
    at Object.onInvoke (core.js:41275)
    at ZoneDelegate.invoke (zone-evergreen.js:363)
    at Zone.run (zone-evergreen.js:123)
    at zone-evergreen.js:857
    at ZoneDelegate.invokeTask (zone-evergreen.js:399)
    at Object.onInvokeTask (core.js:41253)
zone-evergreen.js:2845 POST https://dev.〇〇.com/wp-admin/admin-ajax.php net::ERR_FAILED
scheduleTask    @   zone-evergreen.js:2845
scheduleTask    @   zone-evergreen.js:385
onScheduleTask  @   zone-evergreen.js:272
scheduleTask    @   zone-evergreen.js:378
scheduleTask    @   zone-evergreen.js:210
scheduleMacroTask   @   zone-evergreen.js:233
scheduleMacroTaskWithCurrentZone    @   zone-evergreen.js:1134
(anonymous) @   zone-evergreen.js:2878
proto.<computed>  @   zone-evergreen.js:1449
(anonymous) @   http.js:2601
_trySubscribe   @   Observable.js:42
subscribe   @   Observable.js:28
subscribeToResult   @   subscribeToResult.js:9
_innerSub   @   mergeMap.js:59
_tryNext    @   mergeMap.js:53
_next   @   mergeMap.js:36
next    @   Subscriber.js:49
(anonymous) @   subscribeToArray.js:3
_trySubscribe   @   Observable.js:42
subscribe   @   Observable.js:28
call    @   mergeMap.js:21
subscribe   @   Observable.js:23
call    @   filter.js:13
subscribe   @   Observable.js:23
call    @   map.js:16
subscribe   @   Observable.js:23
(anonymous) @   Observable.js:91
ZoneAwarePromise    @   zone-evergreen.js:960
toPromise   @   Observable.js:89
post    @   article.service.ts:91
async function (async)      
noAnimation @   index-e98418f5.js:89
runTransition   @   index-e98418f5.js:47
async function (async)      
runTransition   @   index-e98418f5.js:44
(anonymous) @   index-e98418f5.js:15
consumeTimeout  @   index-26ec602c.js:2017
flush   @   index-26ec602c.js:2041
invoke  @   zone-evergreen.js:364
run @   zone-evergreen.js:123
(anonymous) @   zone-evergreen.js:857
invokeTask  @   zone-evergreen.js:399
runTask @   zone-evergreen.js:167
drainMicroTaskQueue @   zone-evergreen.js:569
Promise.then (async)        
scheduleMicroTask   @   zone-evergreen.js:552
scheduleTask    @   zone-evergreen.js:388
onScheduleTask  @   zone-evergreen.js:272
scheduleTask    @   zone-evergreen.js:378
scheduleTask    @   zone-evergreen.js:210
scheduleMicroTask   @   zone-evergreen.js:230
scheduleResolveOrReject @   zone-evergreen.js:847
resolvePromise  @   zone-evergreen.js:785
(anonymous) @   zone-evergreen.js:705
step    @   tslib.es6.js:73
fulfilled   @   tslib.es6.js:71
invoke  @   zone-evergreen.js:364
onInvoke    @   core.js:41275
invoke  @   zone-evergreen.js:363
run @   zone-evergreen.js:123
(anonymous) @   zone-evergreen.js:857
invokeTask  @   zone-evergreen.js:399
onInvokeTask    @   core.js:41253
invokeTask  @   zone-evergreen.js:398
runTask @   zone-evergreen.js:167
drainMicroTaskQueue @   zone-evergreen.js:569
Promise.then (async)        
scheduleMicroTask   @   zone-evergreen.js:552
scheduleTask    @   zone-evergreen.js:388
onScheduleTask  @   zone-evergreen.js:272
scheduleTask    @   zone-evergreen.js:378
scheduleTask    @   zone-evergreen.js:210
scheduleMicroTask   @   zone-evergreen.js:230
scheduleResolveOrReject @   zone-evergreen.js:847
resolvePromise  @   zone-evergreen.js:785
(anonymous) @   zone-evergreen.js:705
webpackJsonpCallback    @   bootstrap:25
(anonymous) @   index-index-module-ngfactory.js:1
Show 17 more frames

該当のソースコード

php
1header("Access-Control-Allow-Origin: *");

試したこと

function add_allow_header( $headers ) {
  global $wp;
  if (preg_match ('/wp-json/',$wp->request)) {
      $headers['Access-Control-Allow-Origin'] = '*';
      $headers['Content-Type'] = 'application/x-www-form-urlencoded; charset=utf8';
      return $headers;
  }
}
add_filter( 'wp_headers', 'add_allow_header' );

を追加
WP-APIの「Access-Control-Allow-Origin」をいじった覚書