As long as the WebDAV access is OK (using for example a browser or Nextcloud client) from the same IP address you want to synchronize from(*), this is probably an Android /e/ Drive app problem(**).
*: if many logon attempts were unsuccessful, this IP address may be flagged as “suspicious” by Nextcloud. Please read here: Legitimation issues - #24 by smu44
**: you could try:
- from Settings/Apps (show system), force stop /e/ Drive then clear cache + data
- connect the device to a charger and WiFi network
- reboot to system, unlock device, let it settle for about 1/2 hour