Not all of my customers made it from my desktop version to online. I want even the inactive ones because sometimes they come back and I don't have any history on them

What QB Desktop year version?

I understand how important it is to retain the transaction history for your inactive customers, @eyoung. I'll explain how this works during the migration process.
 

Inactive customers and their transaction history will be included in the migration if they have open balances. Once the migration is complete, these customers will automatically become active in your QuickBooks Online account.
 

However, inactive customers without open balances will not be migrated and won’t appear in QuickBooks Online.
 

For a detailed breakdown of what data is transferred during the migration, you can refer to this resource: Learn how features and data transfer from QuickBooks Desktop to QuickBooks Online.
 

In the meantime, if you still have access to your QuickBooks Desktop account, you can view your inactive customer's transaction history directly from there.
 

Feel free to message us again if you have further concerns.