PostgreSQL CASE expression
You need a string constant there, e.g. 'unpaid'.

Because all branches of a CASE expression must return the same data type, you will also need to cast the stat column to text as well (assuming it's some kind of number as you compare it to one)

case
  when rc.stat = 0 Then 'unpaid'
  when rc.stat = 1 Then 'paid'
  when rc.stat = 2 Then 'dispute'
  else rc.stat::text
end


As you only use = as the comparison operator, you can simplify that expression to: 

case rc.stat
  when 0 Then 'unpaid'
  when 1 Then 'paid'
  when 2 Then 'dispute'
  else rc.stat::text
end