The Mash Stories Competition is open for submissions of flash stories up to 500 words that incorporate the key words Pizza, Selfie, and Corruption into the story. There is no fee to enter and submissions are through Submittable. First prize is $100. The deadline is July 15, 2017. You can find the details here.
Now, this site also has what they call Mash Club which has a yearly fee of $95.88, or $9.99 a month. If you're a member you can submit up to three stories for the competition. You don't have to be a member to submit according to the guidelines.