How do you get “comments” field from vendor record to memo field on vendor bill? I don’t see comments field exposed in “ from” section

Are you trying to do this via workflow? Why not just create header custom field for transaction and source it from entity record.

Yes, I thought about custom field but I wanted to keep it native, if it’s not doable then I will do custom field sourcing

In the record (Join field) you select Vendor and then in the field you can select comments (it may be called note, description or memo also) Lastly, it may not be possible using the joined record because NS will validate the field type. The Comments field is a long text type and the memo is a free text type so they may not be compatible. But you might try a formula. In the formula of your WF try {vendor.comments}, {vendor.note} or {vendor.description}. See if one of those works