help for export/import hikashop to other hikashop

-- HikaShop version -- : 3.5.1
-- Joomla version -- : 3.8.12
-- PHP version -- : 7.1.21

I have 2 site with hikashop business that must be exported in a new third site with hikamarket.
I tried to export the products of 1 shop (3071 products) and to import them in the new site but the import fails.
My steps:
Mass action- Data: Product; Actions: Export a csv file ("select all" for all oprions); check CSV and then "process"

in the new site in Configuration -> file I have "allowed files": zip,doc,docx,pdf,xls,xlsx,txt,gz,gzip,rar,jpg,gif,tar.gz,xlsx,pps,csv,bmp,epg,ico,odg,odp,ods,odt,png,ppt,swf,xcf,wmv,avi,mkv,mp3,ogg,flac,wma,fla,flv,mp4,wav,aac,mov,epub

In "Product" I select "Import" -> Import products from CSV and I select the exported file (in attachment) with the options:
Update products information if the product_code already exists Yes
Create automatically missing categories Yes
Force products to be published if no information is given in the product_published column Yes
Update the product quantity instead of replacing it No
Store images locally Yes
Store files locally Yes
and then IMPORT

I get the error in attachment and the message "500 products found : 0 new products imported, 0 invalid product code, 500 already existing products"
The imported products are 500 (no 3071) all in "product category"

Where I am wrong?

OK, I tried as you suggested but now I get:

Warning
Warning: Failed to move file: to /var/www/vhosts/mydomain/httpdocs/site/images/com_hikashop/upload/hikashopexport.csv

Error
Could not upload the file to /var/www/vhosts/mydomain/httpdocs/site/images/com_hikashop/upload/hikashopexport.csv
FAIL_OPEN

and no products are imported...

Thanks! I am stupid the file is 5 MB and the php upload was setting to 2 MB

I am here again
I exported and imported the products from the 2 hikashop sites to the new site with hikamarket. My problem now is: how do to assign the products to each vendor? I assigned the categories to each vendor, the products are in right categories but from frontend the vendor don't see his products unless I manually edit every products to assign it to the right vendor setting in "custom fields" the vendor. The products are over 3000 for 1 vendor and 1700 for the other vendor I think there is a way to do this automatically but I cannot find the way

Perfect!! Thanks