How to debug lightning-cli invoice I tried:

lightning-cli invoice 100 invoice20190126 payme


and nothing happens. How to debug?
I have copy and pasted the command to my c-lighting node and it works producing the following output: 

lightning-cli invoice 100 invoice20190126 payme
{
  "payment_hash": "af2a2e0a6f4924f755e296c219ade5f2c65616fcec5bb8e62b253b8a71a442cb", 
  "expires_at": 1548528927, 
  "bolt11": "lnbc1n1pwye8cdpp54u4zuzn0fyj0w40zjmppnt097tr9v9hua3dm3e3ty5ac5udygt9sdqgwpshjmt9cqp2rzjqgj8m8dsm7h75az7lry7zc0txghh8tpl3pvdsuctdlvhy4r50nnkkzrgpvqqf0cqqqqqqq05qqqqraqqjq9c06msw62wushzceav74p2zzmznmtud4c3hkw6keqvquxnm6kaxry4rm7aerwppl4jn5xm7tyjxvvyyve5w06slwm7fvxfspx363j9cqcevtr7"
}


Which version of c-lightning are you using? 
Also there was recently a change of the JSON RPC API due to the new plugin system. Could it be that you have not updated lightning-cli but only lightningd?