In Flask, a view must return one of the following:
- a string
- a
Response
object (or subclass) - a tuple of
(string, status, headers)
or(string, status)
- a valid WSGI application
Flask tests for the first 3 options, and if they don’t fit, assumes it is the fourth. You returned True somewhere, and it is being treated as a WSGI application instead.
See About Responses in the documentation.