If a payout has the "pending affiliate input" commission status, this means that your affiliate has not yet input their payout credentials in their interface.
When you enable a manual payout method, your affiliates have to enter their payout credentials for the enabled solutions in order for you to send them payouts.
Affiliates are automatically notified of this by email, and are sent instructions on how to access their interface and input their credentials. Until an affiliate inputs their credentials, you won't have any way to send them their payouts.
If an affiliate hasn't input their payout credentials for a long time, you can send them email reminders to nudge them to input their info.
Please note: if you use a quick payout method instead of a manual method, you will be able to send payouts without any prior affiliate action.