I'm trying to send some bitcoins using bitcoin-cli API, but bitcoin core tells me that Fallbackfee is disabled. How can I set a value for fallbackfee? 
I've tried to specify it like
 *bitcoin-cli sendtoaddress -fallbackfee=someValue* but it didn't work.
 I've also set **true** for *substractfeefromamount* and **false** for *replaceable*