Constant lightning::ln::channelmanager::MIN_FINAL_CLTV_EXPIRY

pub const MIN_FINAL_CLTV_EXPIRY: u32 = HTLC_FAIL_BACK_BUFFER + 3; // 0x0000_0018u32

Minimum CLTV difference between the current block height and received inbound payments. Invoices generated for payment to us must set their min_final_cltv_expiry field to at least this value.