hello, we have tried to install jomsocial update 2.4 but it returns in db500 error into subdomains.

After contacting their support they asked me to contact you to find a way to alter db

this is what they say
"But whatever it is, I can assure you that submitting that MySQL query would solve your problem: ALTER TABLE `[prefix]_community_users` ADD `events` text NOT NULL;"

what do you recon on this?
can you tell me what i should tell them in order to fix this asap?

Thank you

Did you upgraded JomSocial from an older version that had for result to modify the DB layout of JomSocial.

If the answer is yes, you need to re-install JomSocial in each slave site to let it apply the Upgrade of DB layout.

I did try this but it didnt work, same error still occurs.

If you had applied the JomSocial upgrade, you should have the correct table layout.

As you mentioned that you still have the issue, this mean that the upgrade is not performed.

All I can suggest is to verify the JomSocial table structure manually and try identifying which tables have wrong layout.
Perhaps this will help you identifying where JomSocial fail during their upgrade.

I think that JomSocial save a DB layout structure number into the DB to perform their upgrade. Perhaps they have updated the DB layout structure number without applying the upgrade.
Try get more infos from JomSocial.