I receive error on catch TypeError: relativeURL.replace is not a function

I try to save this data…

Each property is transformed in getters and setters by Vue.js

save () {
let scheduleRequests = []
self.schedule.forEach(it => {
  scheduleRequests.push(self.saveEventSchedule({ // <-- VUEX ACTION
    title: it.title,
    tags: it.tags.map(it => it.id)
  }))
})

return axios.all(scheduleRequests)
  .then(results => {
    self.vm.schedule = results.map(r => r.id)
    return self.saveEvent(self.vm)   // <-- VUEX ACTION
      .then(resolve)
      .catch(reject)
  })
  .catch(reject)
}

In my actions …

saveEvent ({ commit }, event) {
  return events.post(event)
    .then(resp => {
      return resp.data
    })
    .then(resp => {
      commit(ADD_EVENT, resp)
      return resp
    })
}

saveEventSchedule ({ commit }, eventSchedule) {
  return eventSchedule.post(eventSchedule)
    .then(resp => {
      return resp.json()
    })
    .then(resp => {
      commit(ADD_EVENT_SCHEDULE, resp)
      return resp
    })
},

And I receive this in catch