RMA refund: You want to return the item for refund. You will be charged 15% restocking fee and shipping is not refundable. (within 30 days of original invoice date, except processors, which is only 7 days).
If RMA type Refund is not enabled to select then that invoice is beyond 30 days and a Refund cannot be selected.

RMA repair: You want to send an item back for replacement (Items older than 90 days maybe replaced with repaired items.)