- /// payable HTLCs except for spontaneous payments, i.e. this should generally only be used for
- /// calls to [`ChannelManager::send_spontaneous_payment`].
+ /// payable HTLCs except for single-path spontaneous payments, i.e. this should generally
+ /// only be used for calls to [`ChannelManager::send_spontaneous_payment`]. If you are sending
+ /// a spontaneous MPP this will not work as all MPP require payment secrets; you may
+ /// instead want to use [`RecipientOnionFields::secret_only`].