Issue: 

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.


Solution:

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)

app/code/Bss/Paymentshipping/Observer/ActivePaymentMethod.php

app/code/Bss/Paymentshipping/Plugin/ShippingMethodManagement.php

+ Flush the cache


If you need any further support, please feel free to contact us.

We'd like to help.