I can't help you with an answer, but I received the exact same error message trying to import an application into our production environment last night.  As with your experience, my production instance is a runtime install.  The workspace is the same on both instances, so I do not believe that to be the root cause in your case. Some data:

• Both my development and production instances are running 18.2.0.00.12.
• I was importing two separate apex applications into production.  Both returned the same error.
• Before starting the install I had successfully imported both applications into my workspace at apex.oracle.com as part of my pre-production testing.

The failing statement and associated error follows:

SQL> prompt --application/create_application

--application/create_application

SQL> begin

  2  wwv_flow_api.create_flow(

  3   p_id=>wwv_flow.g_flow_id

  4  ,p_display_id=>nvl(wwv_flow_application_install.get_application_id,900)

  5  ,p_owner=>nvl(wwv_flow_application_install.get_schema,'###')

  6  ,p_name=>nvl(wwv_flow_application_install.get_application_name,'########')

  7  ,p_alias=>nvl(wwv_flow_application_install.get_application_alias,'F_900')

  8  ,p_page_view_logging=>'YES'

  9  ,p_page_protection_enabled_y_n=>'Y'

10  ,p_checksum_salt=>'F2E1DD6561E5BBE3BA304F40C43A65044B9C840830BD2EAB32677E407E62ED80'

11  ,p_bookmark_checksum_function=>'SH1'

12  ,p_compatibility_mode=>'5.1'

13  ,p_flow_language=>'en'

14  ,p_flow_language_derived_from=>'FLOW_PRIMARY_LANGUAGE'

15  ,p_direction_right_to_left=>'N'

16  ,p_flow_image_prefix => nvl(wwv_flow_application_install.get_image_prefix,'')

17  ,p_authentication=>'PLUGIN'

18  ,p_authentication_id=>wwv_flow_api.id(30266671699127028)

19  ,p_populate_roles=>'A'

20  ,p_application_tab_set=>0

21  ,p_logo_image=>'TEXT:#####'

22  ,p_app_builder_icon_name=>'data_table_icon.png'

23  ,p_public_user=>'APEX_PUBLIC_USER'

24  ,p_proxy_server=>nvl(wwv_flow_application_install.get_proxy,'')

25  ,p_no_proxy_domains=>nvl(wwv_flow_application_install.get_no_proxy_domains,'')

26  ,p_flow_version=>'release 1.0'

27  ,p_flow_status=>'AVAILABLE_W_EDIT_LINK'

28  ,p_flow_unavailable_text=>'This application is currently unavailable at this time.'

29  ,p_exact_substitutions_only=>'Y'

30  ,p_browser_cache=>'N'

31  ,p_browser_frame=>'D'

32  ,p_rejoin_existing_sessions=>'N'

33  ,p_csv_encoding=>'Y'

34  ,p_last_updated_by=>'MMORRIS'

35  ,p_last_upd_yyyymmddhh24miss=>'20190212173908'

36  ,p_file_prefix => nvl(wwv_flow_application_install.get_static_app_file_prefix,'')

37  ,p_files_version=>2

38  ,p_ui_type_name => null

39  );

40  end;

41  /

begin

*

ERROR at line 1:

ORA-02291: integrity constraint (APEX_180200.WWV_FLOWS_FK) violated - parent

key not found

ORA-06512: at "APEX_180200.WWV_FLOW_API", line 4046

ORA-06512: at line 2

Well -- I'm glad you solved your problem... but I'm sorry you solved it *already*.  I opened a ticket with support and got a suggestion... but I can't test it until after business hours tomorrow (next scheduled maintenance window).  I don't really trust the answer 100%, so was hoping you still needed an answer and could test...

I *think* the solution you came up with essentially does the same thing as what I was told to do... by a different route.  In my application export script, the p_workspace_id pointed to a workspace number that exists in my development environment, but not my production one (even though the two are called by the same name).  I sent him the results of the apex_verify script.  From that, he determined the workspace ID number in my production instance and asked me to manually change the ID for the p_workspace_id parameter of the export file to that value.

Since you say that you exported and imported the workspace from your production to your UAT instances... that probably synced the workspace ID numbers between the two.  If you wanted to be REALLY helpful to me, it'd be great if you could check the workspace ID in the application export file that successfuly imported and match it to the one you get from apex_verify.  If the two match, then that pretty much clinches that this is the solution to the error.  I'd feel a whole lot more confident about spending several hours tomorrow afternoon twiddling my thumbs waiting for the maintenance window to open if I knew that was the solution for you.

Thank you... that makes me feel a bit more optimistic about this evening's attempt.