PayPal button Powerstore not working

Hi, Pay pal button with express checkout keeps displaying this message and does not complete

Transaction Not Completed
We're sorry
Your PayPal transaction could not be completed. Please return to checkout and try again.

I have read a lot of posts on the same issue but can not find a fix to the problem that works

Sandbox is unchecked, the user, password and signature are fine

Have also checked the WA_eCart/PP_ECO_Scripts/PP_ECO_PHP.php

and changed - if ($useSB) {
$soapObj->soapURL = "https://api-3t.sandbox.paypal.com/2.0/";
}
to -
if ($useSB) {
$soapObj->soapURL = "https://api-3t.paypal.com/2.0/";
}

Nothing seems to fix it can you help

On the failure page use this code on the top"

<?php

@session_start();

var_dump($_SESSION);

?>

That will display all of the information from the transaction including the full error message. If you send me that (view source on the page first because it will be easier to read) then I can tell you what the issue is.

I can no longer get to the error page as this has come up and none of the site pages are visable.

Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'huffsnpu_1.C2.ContentGroup' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

You can turn off the sql_mode=only_full_group_by setting in your database. You can do that by running this SQL statement from phpMyAdmin:

SET GLOBAL sql_mode=(SELECT REPLACE(@@sql_mode,'ONLY_FULL_GROUP_BY',''));

That just returns

#1227 - Access denied; you need (at least one of) the SUPER privilege(s) for this operation

Contact your hosting company. They should be able to update this setting for you. You may need to do it through the SSH command line.

sorted the problem on server, it was due to sql update last week and not compatible with old version of php and Mysql that powerstore uses, this will need updating?

We will have to do an update to powerstore for php7. The mySQL version wouldn't matter if the settings were the same. You really just had to change that setting, but rolling back to a version with a different setting of course would work as well.

The important part of the error is:
Security errorSecurity header is not valid

This means your username, password, or security key is incorrect. Double check them with your paypal profile and cut and paste to reset them and it should solve your problem.

This did not work, all username, pass and key are fine, re set them just incase and still getting the same error

Can I get FTP access? I can try to debug and see what is wrong.