Hi airpix,
Thank you for dropping by here in the Community. I'm here to help provide insight into entering information in QuickBooks Online.
The fields available in the system includes character limits, and it'll vary depending on the type. You can utilize the Memo field or add a custom one for any extra information you need on the purchase order.
For more insights into the file size and feature limits, here are the steps:
QuickBooks Online file size and feature limits.
In case you want to add custom fields, here are the steps:
- Log into your QuickBooks account.
- Click the Plus sign.
- Select Purchase Order.
- Click the Gear icon in the upper-right corner.
- Click Add another field.
Here's a sample screenshot for your visual guidance:

Fill me in for any additional questions you have regarding the letter limitations. I'm always up to lend a hand.