If the option isn't showing for you to create check the settings on the mini market.
Click on Admin Cogs
icon.Click on Mini Markets.
Click Manage Mini Markets.
Edit relevant mini market.
On details tab scroll down and open up Order Placing settings.
Is the setting ticked for Create Custom /Purchaser products.
If it is enabled, then this will be due to the supplier restrictions. Contact the supplier directly to request this functionality. We are unable to disable this setting.