BHO

That did the trick, thanks!  Re: "Tap on Sync Error, and you will get ..."  it wasn't at all obvious to me that the red "Sync Error" message was a button! A  suggestion: maybe edit the "resolution required" message to "resolution required, tap here", to clarify things for dullards like myself   

Cannot sync from the iOS version of Enpass v6.0.1 (199) (and earlier v6) using Dropbox.  This is under iOS 12.1.2 9 (iPhone Xs).  Dropbox authentication within the Enpass iOS app works just fine, but when the initial sync occurs for the primary vault it results in a red "Sync error / Conflict in syncing data with Dropbox. Resolution required."  ID/Passwords checked, double-checked against other working Dropbox accesses, re-tried multiple times.  Disconnecting and reconnecting do not work; same error occurs (even after force-closing the app).   The iOS Enpass v6 otherwise works fine with its existing set of passwords in the local vault, and with anything I add manually.  Just no sync via Dropbox.

However, the free basic v6.0.2 (240) Win 10 (legacy) desktop apps I use at two different locations work fine with Dropbox: they both happily sync with the same Dropbox account and same credentials as attempted with the above iOS app, for the same primary vault with the same master password.   Dropbox apps\enpass\vault.enpassdbsync exists and is being updated from the desktop apps.

Of note is that this same lashup - same phone w/ iOS 12, same desktops - worked A-OK with Dropbox sync between them with Enpass v5.  All these Enpass v5 installations, sharing a common Dropbox sync, were updated to v6. As I recall, I updated the (purchased) iOS version to v6 first, and immediately had this same Dropbox sync error.   I subsequently updated the (free) Windows 10 desktop versions from v5 to v6 and had no trouble resuming Dropbox sync on and between the desktop apps.  I should mention that retaining or removing the old v5 sync_default.walletx file makes no difference in resolving this issue (it was present along with the vault.enpassdbsync, after the v5->v6 update, until I tried moving it out of the way to see if that helped).

Of further note is that I do have a secondary vault, which is successfully syncing between the iOS phone and the desktops via Google Drive.  However, this Dropbox sync problem on the primary vault was occurring, just as described above, BEFORE the secondary vault was created a day or so ago.

The iOS phone has no content/ad blocker running nor anything of that sort.  Straight-up Safari browser, normal iOS Dropbox app is installed.  I'm trying to avoid losing my vault on the iOS phone, which I anticipate might occur if I uninstall Enpass there and reinstall and STILL can't sync.  But I guess I'll do what I gotta do.   So:

Any advice on what "resolution" is "required" to satisfy the "Sync error / Conflict in syncing data with Dropbox. Resolution required." error?  There doesn't seem to be any error # or logging info that I can see.