How so? I could register even with enabling "Advanced Settings" (because by enabling "Advanced Settings" you will need to enter the details manually but suwako didn't provide them so I had to guess).
If you still have error it's likely you should check how you connect with Gajim/Dino. Launch them from terminal (just type gajim or dino-im in your terminal) to see specific error messages.
Also did you use containers (idk, maybe firejail or any kinds of "sandboxes"), or proxy (like tor) and configured it wrongly?
You can also check if you can use other providers (https://providers.xmpp.net/). If you still can't, you can try Hookipa's as they provide a registration web page.
> How to Apply These Terms to Your New Programs
[...]
> To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively state the exclusion of warranty; and each file should have at least the “copyright” line and a pointer to where the full notice is found.
<one line to give the program's name and a brief idea of what it does.>
Copyright (C) <year> <name of author>
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>.