Failed to contact GPCloud server

Hello,
GanttProject is totally new for me. I would like to test the cloud service.
GanttProject Desktop is installed. GanttProject Cloud account is activated, project is created and team members are invited.
But GanttProject Desktop is endless checking the cloud token.

Maybe the firewall? Before i call the firewall-admin, i would like to know if there is a documentation for the needed ports, etc. I could not found this informations.
Below you found the failure notice in the log-file.

Sep. 06, 2022 11:26:19 VORM. net.sourceforge.ganttproject.GPLogger log
INFORMATION: Starting RSS check…
Sep. 06, 2022 11:27:00 VORM. biz.ganttproject.storage.cloud.GPCloudSignupPane$tryAccessToken$1 invokeSuspend
SCHWERWIEGEND: Failed to contact GPCloud server
java.net.SocketTimeoutException: connect timed out
at java.base/java.net.PlainSocketImpl.waitForConnect(Native Method)
at java.base/java.net.PlainSocketImpl.socketConnect(Unknown Source)
at java.base/java.net.AbstractPlainSocketImpl.doConnect(Unknown Source)
at java.base/java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source)
at java.base/java.net.AbstractPlainSocketImpl.connect(Unknown Source)
at java.base/java.net.SocksSocketImpl.connect(Unknown Source)
at java.base/java.net.Socket.connect(Unknown Source)
at okhttp3.internal.platform.Platform.connectSocket(Platform.java:130)
at okhttp3.internal.connection.RealConnection.connectSocket(RealConnection.java:263)
at okhttp3.internal.connection.RealConnection.connect(RealConnection.java:183)
at okhttp3.internal.connection.ExchangeFinder.findConnection(ExchangeFinder.java:224)
at okhttp3.internal.connection.ExchangeFinder.findHealthyConnection(ExchangeFinder.java:108)
at okhttp3.internal.connection.ExchangeFinder.find(ExchangeFinder.java:88)
at okhttp3.internal.connection.Transmitter.newExchange(Transmitter.java:169)
at okhttp3.internal.connection.ConnectInterceptor.intercept(ConnectInterceptor.java:41)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:142)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:117)
at okhttp3.internal.cache.CacheInterceptor.intercept(CacheInterceptor.java:94)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:142)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:117)
at okhttp3.internal.http.BridgeInterceptor.intercept(BridgeInterceptor.java:93)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:142)
at okhttp3.internal.http.RetryAndFollowUpInterceptor.intercept(RetryAndFollowUpInterceptor.java:88)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:142)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:117)
at biz.ganttproject.storage.cloud.HttpClientOk$$special$$inlined$apply$lambda$1.intercept(GPCloudHttpImpl.kt:392)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:142)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:117)
at okhttp3.RealCall.getResponseWithInterceptorChain(RealCall.java:229)
at okhttp3.RealCall.execute(RealCall.java:81)
at biz.ganttproject.storage.cloud.HttpClientOk.sendGet(GPCloudHttpImpl.kt:404)
at biz.ganttproject.storage.cloud.GPCloudHttpClient$DefaultImpls.sendGet$default(GPCloudHttpImpl.kt:372)
at biz.ganttproject.storage.cloud.GPCloudSignupPane.callAuthCheck(GPCloudSignupPane.kt:138)
at biz.ganttproject.storage.cloud.GPCloudSignupPane.access$callAuthCheck(GPCloudSignupPane.kt:51)
at biz.ganttproject.storage.cloud.GPCloudSignupPane$tryAccessToken$1.invokeSuspend(GPCloudSignupPane.kt:120)
at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:571)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:750)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:678)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:665)

It uses HTTPS, port 443.
Perhaps it just timed out because of whatever reason, and did not handle this properly. Did you try restarting?