Make payment 'required' at registration

There shouldn't be a "gid" column in your database. Only "gids" exists on our UserTable object just to pass along to Joomla for usergroup storage in _usergroups, but it does not exist and should not in the database. If you have an actual "gid" or "gids" column in _comprofiler or _users then please delete it as that sounds like something leftover from a migration

I've been running this site using CB since 2016 without any of these issues - this seems to be a result of upgrading Joomla to 5.4.3?

It sounds like the migration from either Joomla 3 to 4 or 4 to 5 may have caused some possible problems then. Within System > Maintenance > Database see if any database checks are failing and if so run their fix processes. Within CB > Tools go through each of the database check tools and apply any necessary fixes.

Did you use some sort of migration tool by chance? If so that might be the root of your problems here and will probably need to do some manual cleanup of your tables by comparing your table structure to a clean installs table structure. I can provide clean _comprofiler and _users table structure screenshots if you'd like.

I am now getting to the subscription page, but only one of the plans is available; I have 4 plans all marked 'exclusive... but one mandatory'

Be sure your access permissions are set within your plan correctly under the Access tab. Note "Visible for Access Level" and "Visible for Group (and above this group)" should both be set. So if you want the plan public be sure both are set to "Public".

CB 2.11.0+build.2026.01.12.21.55.56.a25ef0f6c
I did the 'migration' to 5.4.3 manually in October 2025; it does appear to have after that the current problem arose.

'All database table structures are up to date.' (system >manage>database)
It would help to have the table structures you mention.

All subscription plans have the correct Access settings; published; accept new; visible;access=public.
Running the database checks in CB management produced only field-type changes in the mailer plug-in, which I corrected.
 

It would help to have the table structures you mention.

Below is clean table structures for both CB and Joomla's user tables.

_comprofiler
 

Note you may have additional fields here as it will also contain fields you've created and those from plugins. Your custom fields typically will all be prefixed with "cb_" so any fields without that prefix may not be necessary anymore and can provide guidance if you have any without "cb_" that aren't in the above screenshot.

_users
 

All subscription plans have the correct Access settings; published; accept new; visible;access=public.

Any other conditions or settings on the other plans that differ? For example are they set to allow registration under the Workflows tab?

I've temporarily suspended new registrations so that the rest of the site remains available;
when a new user signs up, the tabs on the registration form are available, including the full list of plans on the 'subscription tag', with the default one being selected; however the user can click the 'sign up' button on the contact info tab without viewing the subscription tab; it is then that only the default plan appears

I'm not sure I understand. They don't select a plan after clicking sign up. Plan selection is done during registration. If they click sign up then the default selected plan is the plan they will be given. That is working as intended. Set "Selected by default" to "No" for your plans under the Workflows tab if you want them to be sure to select the correct plan before proceeding with registration.

that's the solution; thanks. I'm pretty sure no changes were made during the latest migration but the registration process is now 'working as intended'; (I deleted the gid field from the Users table - everything else seemed OK)