They're wrong. It can't be paid on-line. You'll have to give an envelope to the bishop.
If they say differently, have them show you.
There is a section for "Other", but it only lists the accounts that are automatically swept to Church Headquarters. It doesn't show the Authorized Member Activities.
Have you searched the
Help Center? Try doing a Google search and adding "site:churchofjesuschrist.org/help" to the search criteria.
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Profile to include your general location.