Thanks for joining the thread @gsb06,

This issue only occurs if there are problems with the table/field of mapping. You can try to remove all the mappings, then add it again one by one. To isolate the cause of the problem.

You can refer this link to learn more about importing your customized template: Import custom form styles for invoices or estimates.

Also, if you need other references for invoices and estimates in the future, please feel free to access our site: QuickBooks Online Help Article.

Fill me in if you need more help by leaving a comment below. I'll be around in the Community to help. Take care and have a great day!