Non inventory item to be changed to inventory item. quickbook asking start date and details updated and it is not accepting.

I'm here to help with your QuickBooks concern, @Cityconect.

Can you share with us the error message you're getting when changing the item type? This will help us in determining the cause of the issue and providing you the best solution.

I've tried changing the non-inventory item to an inventory item using my QuickBooks sample account and also received an error message. The error usually occurs once you set up a wrong inventory start date. 

This is the exact error that I've received "Please select an inventory start date that comes after the most recent transaction that used this item".

If you're getting the same issue, I'd recommend setting up the inventory start date next to the day of your most recent transactions (non-inventory sales). This way, you can successfully change the item. 

You can check out the image below for further details. 

After checking the screenshot above, you can follow these steps to change a non-inventory item to an inventory item: 

1. Go to Settings ⚙ and select Products and Services.
2. Find the non-inventory item you want to change.
3. Click Edit in the Action column and select Change type.
4. Choose Inventory, then set up the item as an inventory item. Make sure to select the correct start date.
5. Once done, select Save and Close.

You can also check this article for further guidance: How to change product or service item type in QuickBooks.

Let me know how else I can help you with QuickBooks by adding a comment below. I'm more than happy to lend a helping hand. Have a wonderful day and stay well.