I would recommend that you take this up with the Mendix academy directly (academy@mendix.com), but I think I can guess their answer...
But it is as for most exams, if you subscribe and do not pass (your motivation letter being one of the criteria in this case), you will not get a refund.
Hi Sabita,
Just to complement some information about the requirements for requesting an Expert certification:
"Prerequisites: You have obtained your Mendix Advanced Developer certificate."
You probably have the certification, but in case not, please check that requirement and the following:
Mendix Expert Certification information
Best regards!