procedure.query() "Invalid request body"

[TheBigMemph]

I have a behavior that I can't explain at the moment.

This is a minimal reproduction:

Mutation Test:

//lib/trpc/routes/test.ts
import { t } from '$lib/trpc/t'

export const test = t.router({
    test: t.procedure
        .mutation(() =>
            `test successfull`
        )
})

I call this in a component:

const test = await trpc().test.test.mutate();
console.log(test);

Output Success:

test successfull

---

Query Test:

//lib/trpc/routes/test.ts

import { t } from '$lib/trpc/t'

export const test = t.router({
    test: t.procedure
        .query(() =>
            `test successfull`
        )
})

Call:

const test = await trpc().test.test.query();
console.log(test);

Output:

TRPCClientError-fef6cf44.mjs:26 Uncaught (in promise) TRPCClientError: Unexpected token 'I', "Invalid request body" is not valid JSON
    at _TRPCClientError.from (TRPCClientError-fef6cf44.mjs:26:16)
    at httpUtils-ad76b802.mjs:125:36

No query is working, but mutation is working fine.
I have a project running fine with query. Only difference are package versions of svelte etc.

After some testing typescript doesn't accept the transformer in the createTRPCClient anymore (in t.ts it's accepting it):

import type { Router } from "$lib/trpc/router";
import { createTRPCClient, type TRPCClientInit } from 'trpc-sveltekit'
import transformer from 'trpc-transformer';

let browserClient: ReturnType<typeof createTRPCClient<Router>>;

export function trpc(init?: TRPCClientInit) {
    const isBrowser = typeof window !== 'undefined';
    if (isBrowser && browserClient) return browserClient;
    const client = createTRPCClient<Router>({ init, transformer });
    if (isBrowser) browserClient = client;
    return client;
}

It says:

The type "typeof SuperJSON" cannot be assigned to the type "DefaultDataTransformer".
  The following properties of the type "CombinedDataTransformer" are missing in the type "typeof SuperJSON": "input, output".ts(2322)

Thanks in advance!