LoadCentral 101: 'Cannot proceed. Device not allowed 300'
meaning you already used the application before with your username on other device (1 LoadCentral account : 1 android app)

or na reformat yung device na may installed retailer app

What to do? -> Send an the following details to techsupport@loadcentral.com.ph:
- Username/ registered mobile number
- Valid ID
- reason why you experienced the error

Source: MOL LoadCentral