Hello @UgurU, and welcome to the community!
Thanks a lot for pointing our attention to this problem and for its documented explanation. I wasn’t aware of this issue so I really appreciate your notice. Let’s try to see if we can help.
From the error your detailed it seems it would need to switch to using ACMEv2, so let’s first try to focus on that. I’m personally not familiar with HAProxy, but it seems to be able to use ACMEv2 if configured to do so. I would recommend to have a look their related announcement to see how to do so (linked below) in case some edits in configuration files will fix the issue. As a reminder, these configuration files should be located in the shares you used while installing the rock-on.
The author of the rock-on, @dilli may be able to help as well in case he can see this message. I do notice, thanks to you, that this image hasn’t been updated in several years so it may be wiser to switch to a more recent and supported alternative.
In this context–and as recommended on the HAProxy docker image documentation–would your need be met by using Nginx, for instance? @HBDK recently shared a rock-on for running the Nginx reverse-proxy with included letsencrypt support; this seems like a possible fit for your needs. Please see his message linked below for further details:
Sorry I can’t provide a much clearer help for now, but I hope this will at least help you progress on this issue.