Any person with access to the company space can invite other members to the space but only the space administrator can accept or reject new applications for a membership. You can make the space fully open by disabling moderation of new members.
Adding new participants to the mobile application
In the section "My space" go to "Participants".
1. Choose “Invite people to the company”.
2. After the participant fills out the application, the space administrator will need to approve it.