Can’t add pending members

Please help! I need to sort this out asap. I created a Google Group and invited people. Half were instantly made members and the other half are listed as “pending members.” I do not know why this happened AND I do not know how to make them members. I’ve tried classic and new.

What do I do to make them members?? How do I avoid this in the future?
Thanks,
K

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Author: Kim B