This is a relatively minor oversight but it will save newcomers (like me) some time if we add a step in the Flexinode install documentation that instructs the user the enable the 'administer content types' permission (see my suggested '3.5' below)

3) Enable the flexinode module in Drupal, at:
administration -> site configuration -> modules

3.5) Grant your user role the permission to administer content types at:
administration -> users -> configure -> permissions -> administer content types

4) Create new flexible content types, at:
administration -> content -> content types -> add content type