Hi @dianiss1050 ,
Can you provide a little more details what you meant by setting "incremental forever" backup (level=i)"?
In general, here's a guide on setting up NDMP backup : https://www.veritas.com/content/support/en_US/doc/24427212-127304472-0/v14998369-127304472
There may be some configuration required on the HNAS and then you need to tell NetBackup to use that particular level. This is done in the backup selection list for the policy.
Refer to the PDF doccument found at this link and the relevant section for HNAS devices. It should explain everything. https://www.veritas.com/content/support/en_US/article.100016340