How do I call and add multiple parameters from API to url in C#

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C#

I have multiple organizational URI's that need to be called into a URL. I have a button opening a new page with list of "agents" who are from different organizational units.

Below I've called from unit 474 from the API.

public async Task<List<Agent>> GetAgents()
    {
        var result = await Helper.GetAsync<AgentSearchResult>($"{_propertyApiSettings.BaseUrl}beta/Staff?organisationalUnitUri=/OrganisationalUnit/474", config: await GetHeaders());
        return result.Result.Results;
    }

What do I need to add to include another organizational unit? For example 123.

What I have tried:

public async Task<List<Agent>> GetAgents()
    {
        var result = await Helper.GetAsync<AgentSearchResult>($"{_propertyApiSettings.BaseUrl}beta/Staff?organisationalUnitUri=/OrganisationalUnit/474&organisationalUnitUri=/OrganisationalUnit/123", config: await GetHeaders());
        return result.Result.Results;
    }