i have the following code

```
var UUID = "ExampleX";
var NumID = "ExampleY";
var Payload = string.Format("{\"API1\":{\"API2\":\"API3\",\"API4\":5},\"API6\":\"{0}\",\"API7\":\"{1}\",\"API8\":\"API8\"}",UUID,NumID);

```

i'm trying to replace the input for {0} and {1} with UUID and NumID but i kept getting the following Error

```
Input string was not in a correct format.

```

i'm still learning how to code any help is appreciated