Getting failed to verify challenge error

[monke8555]

I'm trying to write an implementation of the authorization flow in C# using the Web API, as no official SDK exists, and I followed all the steps and this is the error I always get:
{"status":401,"error":"access_denied","sub_status":1005,"error_description":"Unable to verify challenge with id 10e75510-c4b1-4022-a685-fed26f0e04e6"}

I'm POSTing all the values properly:
string response = await "https://auth.tidal.com/v1/oauth2/token"
.PostUrlEncodedAsync(new {
grant_type = "authorization_code",
client_id = clientId,
code = authCode,
redirect_uri = redirectUri,
code_verifier = codeVerifier
})
.ReceiveString();

But I still get the error all the time