How can I migrate data from my QB for Mac desktop app to QB online if I get the "Error while fetching migration data from JSON fileError in processing data"?

We can resolve this JSON error by rebuilding the data file and restarting the export process, Jerelyn.

It will take us four steps to get this done.

Step 1: Verify your company data:

1. Select Window, then Close All to close all open QuickBooks windows (reports, transactions, and so on).
2. Select File, then Utilities, then Verify Data.
3. If QuickBooks reports a problem, continue to step 2.

Step 2: How to rebuild your company data to repair problems:

1. Select Window, then Close All to close all open QuickBooks windows (reports, transactions, and so on).
2. Select File, then Utilities, then Rebuild data.
3. If you see the message Rebuild has completed, continue to Step 3.

Step 3: How to verify your rebuilt company data:

1. Select Window, then Close All to close all open QuickBooks windows (reports, transactions, and so on).
2. Select File, then Utilities, then Verify Data.
3. If you see the message QuickBooks detected no problems with your data, continue to step 4.

Step 4: How to start the export process again:

1. Update QuickBooks to the latest release: Select Help, choose Update QuickBooks. Close and reopen QuickBooks to install the updates.
2. Select Company, then Export Company File to QuickBooks Online.
3. Follow the onscreen instructions.

You can also click on this link to see more fixes when getting errors during the conversation. 

Then, follow the steps in this reference to help your convert your company file:Converting a Desktop for Mac file to Online

We are here if you need a hand.