This catches people out, and it is not a fault in your account. The room in a Circle genuinely changes at two moments, and nobody tells you at the time.
While you are getting set up
If you are a family member who joined before your loved one did, your Circle has extra room on us. Nothing is being billed and no clock is running, so the plan's limit is not the right number to enforce yet. You can bring in a sibling while you get things ready.
During the trial
The same is true for the fourteen days. The Circle holds more than the plan covers, because a trial is meant to be tried properly.
Once she has joined and the trial is over
Now the Circle settles to what Essential actually covers: your loved one and one other person. That is the moment the room changes.
Nobody who already joined is ever removed. If four of you were in the Circle, four of you stay. We do not take a seat back from someone who is already using it.
What changes is the next invitation. That is the one that gets refused, or parked for the payer to approve.
What to do about it
Add a seat for the person you want to bring in. It is $10 a month for each of the first three, and $5 a month for anyone after that, and everyone already in the Circle stays exactly where they are.
You can do that from Preferences → Circle.
If an invitation was refused and this explains why, nothing has gone wrong with your account and nothing needs fixing. It is about room, not about you.