Hello,
When your marketplace is configured to let the vendors be paid directly for their sales, you have to remove the ACL for the payment request.
The value is negative because the vendor owns money to the store for its sales. He received directly the money for its orders, including the feed for the store, money that he has to pay back.
But in such kind of configuration, it's not the vendor to ask for a payment request ; the store manager would have to generate some "invoices" that the vendor will be able to pay (it is an HikaShop order with the "pay later" feature).
Now regarding the message, it indicates that the HikaMarket email for the payment request has been unpublished or you do not have configured the destination email.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.