Your listing is active only on the Basic (free) network of partner sites. You are being asked to pay to upgrade and reply to a lead because that lead is from a network that you have not subscribed to.
Trintals will market our property listings on different networks of syndication partner websites. To fill your vacancy faster we temporarily market new listings on one of our paid networks. This gives our landlords information about potential interest in their listing from that network.
If you upgrade to the paid network you will be able to reply to the lead in question and all leads from that network as long as your subscription is active.