Rest API Error:"The parameter Members does not exist in method AddTenantTheme"

Using the following code. 

$colorPairs = @{

        "themePrimary" = "#003538";

        "themeLighterAlt" = "#cbe6e7";

        "themeLighter" = "#a1cfd1";

        "themeLight" = "#7cb8bb";

        "themeTertiary" = "#5ba2a5";

        "themeSecondary" = "#3f8c90";

        "themeDarkAlt" = "#28767a";

        "themeDark" = "#166064";

        "themeDarker" = "#094b4e";

        "neutralLighterAlt" = "#f8f8f8";

        "neutralLighter" = "#f4f4f4";

        "neutralLight" = "#eaeaea";

        "neutralQuaternaryAlt" = "#dadada";

        "neutralQuaternary" = "#d0d0d0";

        "neutralTertiaryAlt" = "#c8c8c8";

        "neutralTertiary" = "#98a9da";

        "neutralSecondary" = "#4863b4";

        "neutralPrimaryAlt" = "#113191";

        "neutralPrimary" = "#002081";

        "neutralDark" = "#001963";

        "black" = "#001249";

        "white" = "#ffffff";

}

$content = @{

    "name" = "MyCustomTheme"            

    "themeJson" = $jsonBody

            } |  ConvertTo-Json

$apiUrl = "https://<<domain>>-admin.sharepoint.com/_api/thememanager/AddTenantTheme"

Invoke-PnPSPRestMethod -Url $apiUrl -Method "Post" -Content $content

Tried many different combinations but kept getting 

Invoke-PnPSPRestMethod: {"odata.error":{"code":"-1, Microsoft.SharePoint.Client.InvalidClientQueryException","message":{"lang":"en-US","value":"The parameter Members does not exist in method AddTenantTheme."}}}

Wondering if somebody can run this code successfully and let me know what I am missing.