The duration GTC day(s) is not available for this listing type, or invalid for category

The error means that you list items under inappropriate for GTC duration either listing type (auction) or category. 

Please note, some of the eBay categories do not support GTC duration.

To solve the problem you should:

- change listing type (from auction to fixed price):

for M2E Pro based on the Magento v 1.x http://docs.m2epro.com/x/PQAJAQ

for M2E Pro based on the Magento v 2.x http://docs.m2epro.com/x/UwItAQ

- change eBay category

or

- change listing duration from GTC to any other.

 

eBay Integration