Problem in giving a user role to our team member

I've ordered and paid a one year licence for Zoom Workplace Pro for two members with a discount for non profit organisations. I only wanted to pay this on behalf of my organisation because others don't have a right to do this. I'm the admin.
I don't need Pro version, so I changed the basic version for myself. I thought that now I can give this Pro version for two team members who need it in their work. The other one went fine but the other one not - the ad says that due to cancellation they cannot proceed. The cancellation might refer to a cancellation they made for a monthly licence of Zoom that they had before. Now it only suggests that they can take a monthly Zoom but we don't want to pay more because we can't use even this that we already paid. 
I wonder what we should do to get this to work?? Please help!