Anyone have any idea on this error? To give you a context I'm trying to create a custom GL of Intercompany transaction. Any help would be greatly appreciated! Thanks.

I ran into this issue a while ago, I needed to turn on Intercompany Time & Expense. https://docs.oracle.com/en/cloud/saas/netsuite/ns-online-help/section_N1476983.html And then select the correct clearing account.

The accounts must have the check for Elimination (at the account record level)

I already check the elimination at account record @Edgar Valdes

What is the

Account Type

of the selected accounts?

To where Edgar is going (I assume): if you are using "real" AP or AR accounts, ie their type is "Accounts Receivable" or "Accounts Payable", the system requires you to tag each line where that account is used with an interco Customer/Vendor respectively. For that reason, I like to use Other Current Asset or Other Current Liability as the types for interco accounts if possible since they don't have that requirement. Depending on your reporting/compliance needs, you may not be able to bypass the interco customers/vendors though.