037833AU is not identified as a CUSIP.

A complete CUSIP is a 9-character alphanumeric code which identifies a North American financial security and consists of three parts:
• A six-character issuer code
• A two-character issue number
• A single check digit.

CUSIP of 6 or 8-character code can be converted to a 9-character code.

In this case, it's a 8-character code. When I try to complete (on https://dsri.github.io/cusip/) with the check digit, I find 037833AU4 but the result still invalid:

>>> ek.get_symbology(['037833AU4'], from_symbol_type='CUSIP')
                             error
037833AU4  No best match available

With a conversion from 6-digits CUSIP code to 9-character, i found 037833100 that gives following result:

>>> ek.get_symbology(['037833100'], from_symbol_type='CUSIP')
               CUSIP          ISIN    OAPermID     RIC ticker
037833100  037833100  US0378331005  4295905573  AAPL.O   AAPL

If Istart from the ISIN code :

>>> ek.get_symbology(['XS1135334800'], from_symbol_type='ISIN')
                      ISIN    OAPermID    SEDOL ticker
XS1135334800  XS1135334800  4295905573  BYM9D14   APCD

The OAPermID 4295905573 identifies the company APPLE and matches with the result of following request based on 037833AU (without AU suffix):

>>> ek.get_symbology(['037833'], from_symbol_type='CUSIP')
          OAPermID
037833  4295905573

@szevak.nzsdejan since this is a content question, I suggest that you should contact your local Thomson Reuters support desk and raise this with them.

Usually, the CUSIP code is included in the ISIN code.
In this case, CUSIP should be 113533480, and the request confirms it exists:

>>> symb = ek.get_symbology(['113533480'], from_symbol_type='CUSIP', debug=False)
>>> symb
                   ISIN           RIC    SEDOL
113533480  XS1135334800  US113533480=  BYM9D14

Could you detail the way you found 037833AU value ?