Passing parameters in R in an api with the Post method?

Friends, I created an api in R using Plumber with the post method. but at the time of calling this api and passing the parameters I'm not getting it, I call it this way:

resp <- POST("http:url", body = list(datainicio = '2018-07-23' , datafim = '2018-07-24'), encode = 'json')
r1 <- httr::content(resp, 'text')

and the error returned is:

  

[1] "{\" error \ ": [\" 404 - Resource Not Found \ "]}".

Thank you