Can't download PDF from rest API. PDF not supported error

EDIT: I was able to "fix" it by returning it as a JSON object and one of the JSON object elements was the base64 encoding of the file. Then I used these 2 methods to convert the base64 encoding to an array and output the file

public Base64ToArrayBuffer(Base64: any)
    {
        var binaryString = window.atob(Base64);
        var binaryLen = binaryString.length;
        var bytes = new Uint8Array(binaryLen);
        for (var i = 0; i < binaryLen; i++)
        {
            var ascii = binaryString.charCodeAt(i);
            bytes[i] = ascii;
        }
        return bytes;
    }

    public SaveByteArray(FileName: string, ByteArray: any, MimeType: string)
    {
        var blob = new Blob([ByteArray], { type: MimeType });
        var Link = document.createElement('a');
        Link.href = window.URL.createObjectURL(blob);
        Link.download = FileName;
        Link.click();
    };

I have the following API call using aadHttpClientFactory which is calling an endpoint that returns a PDF byte array.

In the HttpClientOptions I'm setting the Content-Type to application/pdf and the Content-Disposition to attachment; filename="test.pdf".

When the API call runs the .post() method the res variable returns a 400 error that I put below. Is there somewhere in Azure or SharePoint where I need to allow the PDF content type? I have no issues with my API calls when I return JSON.

Also, I used Postman to test the endpoint using a bearer token and it works successfully and returns the byte array.

{"code":"400","status":"REQUEST_ERROR","errors":["Content type 'application/pdf;charset=UTF-8' not supported"]}

return new Promise<any>(async (resolve, reject) =>
        {
            Context.aadHttpClientFactory
                .getClient(Settings.AZURE_SHAREPOINT_APP_REG_CLIENTID)
                .then((client: any): void =>
                {
                    client
                        .post(url, AadHttpClient.configurations.v1, HttpClientOptions)
                        .then((res: any) =>
                        {
                            resolve(res);                           

                        }).catch(error =>
                        {});
                }).catch(error =>
                {});
        });