Unless settings are tweaked, AFAIK the default Trust Level for getting Invite ability is Trust Level 2
https://meta.discourse.org/t/what-do-user-trust-levels-do/4924/5?u=mittineague
Users at trust level 2 can…
Use the “Invite others to this topic” button for one-click onboarding of new users to participate in topics
Invite outside users to PMs making a group PM
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