Realex RealDirect Payment Module.

[max.emarkable]

Issue is solved for me.
For those who suddenly have same issues.

1. You can change md5 to sha1 functions in file, but if you feel uncomfortable - you can contact realex to enable md5 support back.

2. Adding MERCHANT_RESPONSE_URL field is not required as, you supposedly provided it to realex to put in their system when you set up this payment option.
If you don't know the response url is http://www.mywebsite.com/store/before_process.php as per plugins readme.txt.

3. "transaction is completed but can't return to the merchant website, please contact merchant about this error." - would appear If you are anxious person like me, who puts maintenance page for everyone except couple IPs to avoid people contacting you about sha1hash missing error they got; Maintenance page is issue because Realex checks if response page have any redirects and wont send visitor back to your website if they will spot any.