I Need help with Error Message: Export limit exceeded. Upgrade to the Export Invoices Add-On for unlimited access. - /v3/doc/create

From the above message I can understand that you have exhausted the limit of creating 3 Free Export invoice.

If you would like to continue using this feature, you will have to upgrade your plan to the Export Invoices add-on for unlimited access. ​

To know more about the Add-on Export feature, kindly contact support by clicking the link below.