Hi everyone,
To preface: I’m not super knowledgeable on the technical side, but very willing to learn. I might be making very dumb mistakes, please bear with me! 
I’m using Nextcloud for a while now for photo’s, files and notes. I use a server through Hertzner storage.
I have now installed the app Tables, because it would be a neat way to keep track of watching/reading recommendations. I have installed it via the webportal very easily and set up my first table without hickups. Then I installed the Tables app on my phone. I could see the table I created, but not the viewings. When I tried adding a row to the table on my phone I got the following error message:
App Version: 1.1.2
App Version Code: 1001002
Server App Version: 27.1.0
App Flavor: fdroid
Files App Version Code: 30260090 (PROD)
OS Version: 4.9.190+(20220817)
OS API Level: 29
Device: KINGKONG_MINI2
Manufacturer: CUBOT
Model (and Product): KINGKONG MINI2 (KINGKONG_MINI2_EEA)
java.util.concurrent.CompletionException: com.nextcloud.android.sso.exceptions.NextcloudHttpRequestFailedException: HTTP request failed with HTTP status-code: 520
at it.niedermann.nextcloud.tables.ui.table.view.ViewTableViewModel.lambda$synchronizeAccountAndTables$0$it-niedermann-nextcloud-tables-ui-table-view-ViewTableViewModel(ViewTableViewModel.java:50)
at it.niedermann.nextcloud.tables.ui.table.view.ViewTableViewModel$$ExternalSyntheticLambda1.get(Unknown Source:4)
at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1627)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
at java.lang.Thread.run(Thread.java:919)
Caused by: com.nextcloud.android.sso.exceptions.NextcloudHttpRequestFailedException: HTTP request failed with HTTP status-code: 520
at it.niedermann.nextcloud.tables.repository.ServerErrorHandler.handle(ServerErrorHandler.java:53)
at it.niedermann.nextcloud.tables.repository.ServerErrorHandler.handle(ServerErrorHandler.java:29)
at it.niedermann.nextcloud.tables.repository.AccountRepository.synchronizeCapabilities(AccountRepository.java:148)
at it.niedermann.nextcloud.tables.repository.AccountRepository.synchronizeAccount(AccountRepository.java:97)
at it.niedermann.nextcloud.tables.ui.table.view.ViewTableViewModel.lambda$synchronizeAccountAndTables$0$it-niedermann-nextcloud-tables-ui-table-view-ViewTableViewModel(ViewTableViewModel.java:46)
… 5 more
Caused by: java.lang.RuntimeException:
… 10 more