GET request works in browser and postman, but I get unauthorized when using httpclient and resthsharp

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C#

API

ASP.NET-Core

I am issuing a request via Postman

"https://APIKEY:PASSWORD@myexampledomain.myshopify.com/api/2021-04/custom_collections.json"

and I get a true response:

{
    "custom_collections": [
        {
            "id": 264277491901,
            "handle": "baran-kategori",
            "updated_at": "2021-04-08T18:05:03+03:00",
            "published_at": "2021-04-05T16:40:08+03:00",
            "sort_order": "best-selling",
            "template_suffix": "",
            "published_scope": "web",
            "title": "Baran Kategori",
            "body_html": ""
            
        },
        {
            "id": 264276377789,
            "handle": "category1",
            "updated_at": "2021-04-06T14:49:26+03:00",
            "published_at": "2021-04-05T16:12:36+03:00",
            "sort_order": "best-selling",
            "template_suffix": "",
            "published_scope": "web",
            "title": "Category1",
            "body_html": ""
            
        },
        {
            "id": 264362623165,
            "handle": "nike",
            "updated_at": "2021-04-08T18:05:03+03:00",
            "published_at": "2021-04-06T16:17:49+03:00",
            "sort_order": "best-selling",
            "template_suffix": "",
            "published_scope": "web",
            "title": "Nike",
            "body_html": ""
            
        }
    ]
}

when attempting to do the same GET through httpclient or restsharp, I am getting a 401 unauthorized.

{StatusCode: 401, ReasonPhrase: 'Unauthorized', Version: 1.1, Content: System.Net.Http.HttpConnectionResponseContent, Headers: { Date: Thu, 08 Apr 2021 16:12:33 GMT Transfer-Encoding: chunked Connection: keep-alive X-Sorting-Hat-PodId: 188 X-Sorting-Hat-ShopId: 56072536253 Referrer-Policy: origin-when-cross-origin X-Frame-Options: DENY X-ShopId: 56072536253 X-ShardId: 188 WWW-Authenticate: Basic Realm="Shopify API Authentication" Content-Type: application/json; charset=utf-8 Content-Length: 89 }}

What I have tried:

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