I cannot create a team.

Whether or not team-up function is enabled depends on the competition type. When it comes to the competition where the function is enabled, you can see the Team Up button appearing next to the Submit button. Note those one of the following conditions applies are not allowed to join a team when:

the user has already teamed up.
the user already belongs to another team.

Please also not that in order for one to join a team, it must

be a solo participant.

Note that a team should be created for each competition even though it has the same team members.