How to post a Tweet using Twitter v2 API?

[helpermethod]

Hi there!

I'm trying to perform a .postTweet() but I'm always getting a 401 Unauthorized.

This is how I'm setting up the client (in Kotlin, but this shouldn't make a difference):

val twitterClient = 
    TwitterClient(
        TwitterCredentials(
            apiKey,
            apiSecretKey,
            accessToken,
            accessTokenSecret,
            null,
        ),
    )

twitterClient.postTweet("Hello World!")

I suppose there is something wrong with my credentials, but I can't figure out what.

[helpermethod]

Sorry, my fault, everything works perfectly.