JSONSerialization Invalid type in JSON write (_SwiftValue)

Question

Why does the following code give me the error:

Invalid type in JSON write (_SwiftValue).

The error is thrown on this line:

Answer 1

Had the same problem and error as you! FINALLY found the issue...

My code:

params = [
    "gender": request.gender.first ?? "",
    "age": 15
]

Problem: Even though request.gender.first ?? "" returns a string, its a type of String.Element, which ANY JSONEncoder or JSONSerialization cannot encode (and is not in the list of types it can handle, according to documentation).

Solution:

params = [
    "gender": request.gender.first?.description ?? "",
    "age": 15
]

Typically, just make sure its a string or an appropriate number the Encoders can handle...