Hi,
Checking the code of the SIPS ATOS v2 payment plugin, I see there is an extra space for the test URL for BNP on the line:
'bnp_test' => ' https://payment-webinit.simu.mercanet.bnpparibas.net',
which should actually be:
'bnp_test' => 'https://payment-webinit.simu.mercanet.bnpparibas.net',
in the file plugins/hikashoppayment/atossips/atossips.php
Please change that and try again.
If it helps, then this is the problem.
If not, then please check with the BNP merchant tech support to see if you're using the correct solution and whether the URL is the correct one.