Having trouble referencing a cell in external workbook (Ubuntu 20)

I’m using LO Calc 6.4.6.2 on a Ubuntu 20 system. I’m trying to reference a cell in an external workbook. Opening the workbook and clicking on the “Allow Updating” button results in the error #REF.

The reference definition is:

='file:///home/glb/Documents/Business_Financial/Business/2021/business_2021_Budget.ods'#$'January 2021'.J12

J12 is a numeric cell as is the receiving cell.

The directory structure of /home/glb/Documents/Business_Financial is:

./Business:
total 19
drwxrwxr-x 2 glb glb 5 Jan 27 16:12 2021

./Business/2021:
-rwxrwxr-x 1 glb glb  24983 Jan 27 15:38 business_2021_Budget.ods

./Personal_HH:
drwxrwxr-x 2 glb glb     4 Jan 27 15:43 2021

./Personal_HH/2021:
total 45
-rwxrwxr-x 1 glb glb 43659 Jan 27 15:43 Personal_Budget_2021.ods

Personal_Budget_2021.ods is the receiving file while business_2021_Budget.ods is the sending file.
Can anyone point me in the correct direction ?

Thanks

Duplicate of Calc 6.4.6 - Can't figure external references - googling and docs no help

Please delete this one and keep track on 294949