This article also explains why users with the role permission to accept invoices do not see the accept invoice button in the invoice tab.
The following steps outline how to activate an approval override for order placed through MP Scan by the user's approval limits.
At the top, click the Admin Cogs
icon. Click Mini Markets, then click Manage Mini Markets.
Edit the required mini markets, and stay on the Details tab, scroll down to the bottom and expand the MP Scan section by clicking on the word.
Use the Check box to activate or deactivate the setting Accept invoice permission override.
Click Update at the bottom to save the changes.