We have established that the module Magento 2 Shipping and Payment Method per Customer Group v1.1.6 but it is causing an "invalid state change requested" error at checkout for any logged in customer.
The issue is cause due to our module's bug.
To solve it, please follow our guide below.
+ Edit and apply two files on the site (refer to the attachments)
+ Flush the cache
If you need any further support, please feel free to contact us.
We'd like to help.