C# string interpolation-escaping double quotes and curly braces

It seems that you have missed escape for the products and query objects:

$@"{{
    ""name"":""{taskName}"",
    ""products"": [
        {{""product"": ""ndvi_image"", ""actions"": [""mapbox"", ""processed""]}},
        {{""product"": ""true_color"", ""actions"": [""mapbox"", ""processed""]}}
    ],
    ""recurring"":true,
    ""query"": {{
        ""date_from"": ""{dateFromString}"",
        ""date_to"": ""{dateToString}"",
        ""aoi"": {polygon}
    }},
    ""aoi_coverage_percentage"":90
}}";

Just in case someone else is considering doing the same, it would be better to create an anonymous type and serialize it to json for two reasons:

1. it's a lot more readable and maintainable (how long would it take someone to change the code because the json structure has changed while keeping all escapes in order -- especially if there are no unit tests?)
2. it's a lot more reliable (what if taskName has a double quote?)

Below uses json.net for serialization.

var jsonObj = new {
  name = taskName,
  products = new[] {
    new { product = "ndvi_image", actions = new [] { new { mapbox = "processed" } },
    new { product = "true_color", actions = new [] { new { mapbox = "processed" } }
  },
  recurring = true,
  query = new {
    date_from = dateFromString,
    date_to = dateToString,
    aoi = polygon
  },
  aoi_coverage_percentage = 90
};

var jsonString = JsonConvert.SerializeObject(jsonObj);

In addition to @"..." and $"..." C# supports $@"..." strings, which is what you are looking for when you build multi-line string literals that need to be interpolated:

$@"{{
    ""name"":""{taskName}"", 
    ""products"": [    
                {{""product"": ""ndvi_image"", ""actions"": [""mapbox"", ""processed""]}}, 
                {{""product"": ""true_color"", ""actions"": [""mapbox"", ""processed""]}}
              ], 
    ""recurring"":true,
    ""query"":   {{
                    ""date_from"": ""{dateFromString}"",
                    ""date_to"": ""{dateToString}"",
                    ""aoi"": {polygon}
                }},
    ""aoi_coverage_percentage"":90
}}";