Invited a friend but they can't join because they're not on the "Whitelist"

Hi,

A friend of ours can't join because they're not on the "whitelist" but we don't have any control over the whitelist. Her username is Merga and mine is PaperSailboat - I am the owner on the server. I expect that anyone I invite should be permanently allowed to use the server. If you do not wish for me to look for other services, I expect this to be remedied ASAP.

Thank you,
A concerned customer