"Complete task" not including all the necessary information when request id is not in accepted mode

## Description
As a user,when i try to complete a task I need to know what I did wrong and why what I expected did not happen.

I observed that when a request id is not accepted and a user tries to complete a task (which does not exist, as a task cannot be created) the message is about the wrong task, but it should show the initial problem too, that the relationship is not accepted.

**To Reproduce**
Steps to reproduce the behavior:
1. Send a relationship request from user1 to a user2
2. Do not accept that request from user2
3. Try to complete a task (the number will be random as a task cannot be created)
4. See the error message, about the task not existing, but not about the relationship not having been accepted

**Expected behavior**
The message should inform the user trying to complete the task that the relationship is not accepted too.

**Screenshots**