Please check the related Payment Form->Recurring Payments Type field. Check if the Recurring Payments Type is assigned to Variable?
Variable means the Payment Txn gets generated. Then you can update the Amount and change the Status to "Payment Start" to initiate the transaction. This is useful for us internally as an example. We generate the transaction, run a process that calculates the monthly charge based of the number of transactions a customer has completed, then change the status to payment Start to charge the customer.
If the above is the case, you can change the status to Payment Start.
Then, update the Payment Form "Recurring Payment Type" to "Regular" for future processing.
If the above is not the case, please check the Error logs for a date/time created that is similar to the Payment Txn generation.