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.