If you can't find the user in the list of users when trying to give him/her briqs. Check with your admin if the user has been invited to Briq. The admin can easily check this information in his/her Members section.
If you are using Briq with slack, make sure the concerned user is a regular slack member. Only regular slack member can be invited to Briq. So, if the user in question is only an invited member on your slack, you need to change his/her status to regular member before s/he can be invited on Briq.
If you are still encountering difficulties, please contact us.