All accesses denied in Webdav and Desktop client but all works fine in browser

Hello everyone,

I am having some trouble lauching the desktop client. I looked in the manual and made the Webdav test : it doesn’t work (from different computers with different logins).
The manual says to “ensure that [my] authentication backend is configured properly”. As we say in France, “I understand quickly but one has to explain things to me for a long time” : I have no idea how to do that, I am only creating a website for a local nonprofit organization and don’t have a lot of programing skills. Also, I looked ad this page to try to fix it but I am not sure what to begin with (does someone know if there is an equivalent for Litmus ?)

Here is the client log (server is too big to be posted apparently and I can’t upload text files)

02-11 10:11:52:215 2280 OCC::OwncloudSetupWizard::slotConnectToOCUrl: Connect to url: ""
02-11 10:11:52:221 2280 OCC::OwncloudWizard::appendToConfigurationLog: Setup-Log: "Tentative de connexion à Nextcloud sur …"
02-11 10:11:52:222 2280 OCC::AbstractNetworkJob::start: !!! OCC::PropfindJob created for “” + “/” "OCC::OwncloudSetupWizard"
02-11 10:11:55:559 2280 OCC::HttpCredentials::slotAuthentication: Stop request: Authentication failed for ""
02-11 10:11:55:560 2280 OCC::AbstractNetworkJob::slotFinished: void OCC::AbstractNetworkJob::slotFinished() QNetworkReply::NetworkError(OperationCanceledError) “L’opération est annulée” QVariant(Invalid)
02-11 10:11:55:561 2280 OCC::PropfindJob::finished: PROPFIND request not successful, http result code is 0 “”

Thanks a lot to anyone who can help :).