A few customers on 2021 R1 (12.0.25) have reported below issues:

Issue 1:

If the field "Trade name 2" is empty, you can enter a text and save the customer record. But after saving, the field only contains the value "0". 

Issue 2:

When the field "Trade name 2" contains the value "0", you can enter a text in the field, but the save button is not being enabled. You cannot save the customer.

A hotfix has been released to resolve this issue. To obtain the hotfix, please contact your local support team, referencing bug "X3-235347" and your X3 release in your request for the hotfix or download from the Sage FTP site patches folder for 12.25 / 2021R1

Please test and apply the hotfix from X3 folder:

WX_236358_R090_025  (Compatible only with 2021 R1 where the issue is experienced)

The actual fix is part of 2021 R2 (12.0.26)