Most often, this is caused by not configuring the module with the necessary Stripe API keys (both publishable and secret) on the Stripe tab.
In some cases, other extensions may interfere with the EasyPay module's operation. We reference Stripe's javascript library directly and anything that removes Javascript from the page as either a security measure or to "optimize" the site may conflict with Stripe EasyPay. Some common extensions we've found that may interfere with the module's operation are:
- JCH Optimize
- Sucuri
Most likely, these extensions have a configuration setting to allow Stripe EasyPay to operate normally, but you will need to consult with their support to determine whether you can whitelist the Stripe javascript library.