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This error message indicates a problem with the remote WebDAV server. It slammed the door on our face before we could even tell it who we are and what we want.

As it happens, I use pCloud too -- I love their crypto folder feature :) However, pCloud does not officially offer a WebDAV connector. The only reference I can find to the WebDAV enpoint you are using is a third party post from nearly 3 years ago claiming that WebDAV is supported by pCloud.

Out of curiosity I tried using the purported WebDAV endpoint with my account on an application I know works with WebDAV (KDE's Dolphin file browser). It cannot connect to that WebDAV endpoint, crashing with an SSL error. The same application works great with other WebDAV servers, e.g. a NAS I have at home.

So, it looks like the problem is that pCloud does not, in fact, support WebDAV. Implementing an Akeeba Backup connector for pCloud is on my to-do list but I don't have a good estimate of how long it will take to share with you.

The page you reference is not a page in pCloud's own site. It proves nothing to me except that a third party claims that pCloud supports WebDAV.

Even if pCloud supports WebDAV the error message does not come from Akeeba Backup. Akeeba Backup uses PHP's cURL extension. In turn, this uses the cURL library (libcurl). In turn, it uses OpenSSL to connect to the remote endpoint. The error comes from OpenSSL, i.e. three layers removed from any code we can touch.

If you are absolutely certain that pCloud does support WebDAV you need to talk to your host. If you look up the error code at cURL's site it is describe as "Unknown SSL protocol error in connection". Ruling out the possibility that the remote end (pCloud) does not support WebDAV and HTTPS we are left with two explanations. Either your host is blocking the connection to webdav.pcloud.com on their firewall OR their cURL library is compiled against a very old version of the OpenSSL library. Seeing that the PHP version is decently up to date I don't think it's the latter. So, you need to ask your host to unblock HTTPS connections over TCP port 443 to the host webdav.pcloud.com

I have some more information for you. While pCloud does seem to offer a WebDAV endpoint, it will NOT work if the account has Two Factor Authentication enabled. That was why I could not connect to it with my account. If the account does not have Two Factor Authentication you can, in fact, use the endpoint with WebDAV and it seems to also work with Akeeba Backup.

Since you told me that you could connect to it and transfer files I understand the problem is not Two Factor Authentication. This leaves us with the possibility of a firewall on your host's side. Please do contact your host and ask them to unblock connections over TCP port 443 to host webdav.pcloud.com

Please note that not being able to upload the files to remote storage IS NOT an error condition, it's a warning. Even if the upload fails partially or completely the backup will show as complete. In the worst case scenario, some of the files are fully uploaded to remote storage and some are still on your server. Therefore you have a complete backup set, i.e. the backup is complete. That's what is being reported.

The WebDAV connector does retry up to three times after it sees an error condition from the server. So yes, it is possible that what you saw is a transient warning. The thing is, you told me the upload failed and that's the basis of my replies. If the upload did not fail and you do have these files on pCloud then why are we having this conversation? :)