Problem is with your GET url parameters
Try this url:
127.0.0.1:5000/app-api?store=Play Store&category=Games
You don't need to send single quotes in querystring values i.e
<your-host>/?store=XXXXXX not like this <your-host>/?store='XXXXXX'
Also, filter_by
is used for simple queries, If you want to make complex Queries use filter and for more info go through this StackOverflow question