Are you trying to apply for an extension or making a payment by the due date?  This is what the filing instructions says:

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SMLLCs disregarded for tax purposes will be granted an automatic six month
extension, with the exception of an SMLLC owned by a partnership or an
LLC that is classified as a partnership for California tax purposes, which will
be granted an automatic seven month extension. For more information see
R&TC Section 18567

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In any case, ProConnect will charge for a return once you initiate e-filing, whether for extension or an actual return, or when it's printed.

If it's only for making a payment, you may want to direct your client to the FTB's Web Pay website instead.