Yes, open July for GL (and any other applications you will post in, or all applications) in the fiscal calendar, then post.  You probably want to change the error batch description before you post it.  And don't forget to open August for all apps before you start posting in August.

You need to roll your GL into the new fiscal year via periodic processing.
Do a backup then go to GL periodic processing
Create new year
Do that then you'll be able to post those entries

It seems like the issue you're facing is related to the fiscal period being locked in Sage 300 Premium's General Ledger module. The error message indicates that Period 1 of the fiscal year 2024 is locked in the Fiscal Calendar. This typically occurs to prevent any further changes or postings to a period that has already been closed.

To address this issue and correctly post your AP payments for July, you can follow these steps:

• Verify the Lock Status: Double-check that Period 1 of the fiscal year 2024 is indeed locked in the Fiscal Calendar. Sometimes, these issues can arise due to misconfiguration or misunderstanding.

• Unlock the Period: If you find that Period 1 is locked, you will need to unlock it. To do this, you would generally require appropriate permissions. You can navigate to the Common Services or Fiscal Calendar module, locate Period 1 for the fiscal year 2024, and unlock it.

• Repost the Entries: Once you've unlocked the period, you can go ahead and repost the AP source entries from the GL batch listing that resulted in the error. Make sure to double-check the batch and its entries for accuracy before posting.