Hi Nandini,
If you have different fields name against of the invoices then you need to send them into Batches(Example: - create one batch just for 2-3 invoices and place those invoices which contains Total Amount. And do the similar for others invoices) and train the model against of each different invoices.
Once you will train ML model against of each different set of batches then For the second run you will get a good result of extraction data.
Thanks,Jay------------------------------
Jayvirendra Rawat
Software Developer
Capgemini India Services Ltd.
Delhi
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JAY Rawat
Sr. RPA Developer
Delhi(NCR)
India