2 BOs come into play when sending.
1) you need to FIND that one REST record to make it current
2) you need a BO somewhere to create the reply, and stuff it into a field.
This can be LIRU, for now.
Create a field temp_rest_reply in RegularUser
so that process ends up being
FIND ALL REST_LearningLinq (that the BO with the REST services defined and only 1 record in the file)
FIND RegularUser where RegularUser = LIRU
RegularUser.temp_rest_reply = 'the data i want to post'
REQUEST SERVICE POST_theservicename FROM REST_LearningLinq
And in the POST_theservicename service setup screen, you've checked
(*) Take From Context
and referenced RegularUser and the temp field