When trying to import a journal entry, we keep getting the following error: Invalid custcol_gl_account_lcd reference key "11000" for custcol_lcd 824..... despite this account and the combo being present in NetSuite. We even already have transactions at this combo, so we know it exists in the system. I have attached screenshots as well as the source file.... any ideas?

Try using internal id or at least check the import map

you cant use just the account number as a reference. Either use the full account name with all the hierarchy or internal id or external id (best option)