Install new Payment Method in Store module

I’m trying to add an additional Omnipay payment method in the Store e-commerce module. The code is available at: https://github.com/maclof/omnipay-global-iris

I’ve used composer to rebuild the third_party/store/vendor directory and associated composer files and then uploaded that to the server and then disabled and re-enabled the Store extension hoping that it would pick up the new payment method but it doesn’t show up. The method is included in the installed.json file in vendors/composer along with the other default payment methods which do appear in the Store>Settings>Payment methods in the admin portal.

Any suggestions as to why the payment method isn’t appearing would be much appreciated. Thanks