Create Session => Content-Type is unsupported. You should use application/json instead

https://github.com/clerk/clerk-sdk-java/blob/main/docs/sdks/sessions/README.md#create causes:

"Content-Type is unsupported","long_message":"Content-Type is unsupported. You should use application/json instead.",

ClerksTest > clerkTestingToken() FAILED
    SDKError[requestMethod=POST, requestUri=https://api.clerk.com/v1/sessions/sess_39zfw909Yvg9iEfgxVGM1IC3iDf/tokens, code=415, responseHeaders={:status=[415], cf-cache-status=[DYNAMIC], cf-ray=[9d18d52f1b327a85-ZRH], clerk-api-version=[2025-11-10], content-length=[228], content-type=[application/json], date=[Sat, 21 Feb 2026 20:00:56 GMT], server=[cloudflare], set-cookie=[__cf_bm=n3QrywajChUuzq95LHZs9LQEGEAbiBUXSOnsvYOzg7E-1771704056-1.0.1.1-2Cbe4GAqRt42WHTgNj.ovn4H2GxUhfdHN_hWRcVpP1gGK49gGr_70K97pYTlGZ3GQbzi0uqCtHDIfHWH_XdCE1PdEMlXa0IpI83kYHZvyXE; path=/; expires=Sat, 21-Feb-26 20:30:56 GMT; domain=.api.clerk.com; HttpOnly; Secure; SameSite=None, _cfuvid=SClopz.8P6zvAeeE1aAfZADl7YHmmvqBWnJxWe0nv1c-1771704056345-0.0.1.1-604800000; path=/; domain=.api.clerk.com; HttpOnly; Secure; SameSite=None], x-cfworker=[1], x-clerk-trace-id=[ba15286b6af46c65de478848a7c3cb1f], x-cloud-trace-context=[ba15286b6af46c65de478848a7c3cb1f]}, message=API error occurred, body={"errors":[{"message":"Content-Type is unsupported","long_message":"Content-Type  is unsupported. You should use application/json instead.","code":"unsupported_content_type"}],"clerk_trace_id":"ba15286b6af46c65de478848a7c3cb1f"}]
        at app//com.clerk.backend_api.models.errors.SDKError.from(SDKError.java:35)
        at app//com.clerk.backend_api.models.errors.SDKError.from(SDKError.java:29)
        at app//com.clerk.backend_api.operations.CreateSessionToken$Sync.handleResponse(CreateSessionToken.java:217)
        at app//com.clerk.backend_api.operations.CreateSessionToken$Sync.handleResponse(CreateSessionToken.java:133)
        at app//com.clerk.backend_api.models.operations.CreateSessionTokenRequestBuilder.call(CreateSessionTokenRequestBuilder.java:77)
        at app//dev.enola.common.auth.clerk.Clerks.clerkTestingToken(Clerks.java:100)
        at app//dev.enola.common.auth.clerk.ClerksTest.clerkTestingToken(ClerksTest.java:14)

from:

public static String clerkTestingToken() {
        Clerk clerk = Clerk.builder().bearerAuth(CLERK_SECRET_KEY).build();
        var testUserID = "user_...";
        var sessionID =
                clerk.sessions()
                        .create()
                        .request(new CreateSessionRequestBody(testUserID))
                        .call()
                        .session()
                        .get()
                        .id();
        return clerk.sessions()
                .createToken()
                .sessionId(sessionID)
                .call()
                .object()
                .get()
                .jwt()
                .get();
        // TODO Return a Closeable where close() revokes the token
    }

Intended to be use in an integration test.

Start with CreateSessionTokenRequestBuilder.call and CreateSessionToken.java, where the failing stack trace shows the token request is built and handled. Inspect how the request Content-Type is set, then rerun ClerksTest.clerkTestingToken as the integration check; done means the session token request uses application/json without the 415 error.