Fatal Errors with Payment Gateways

We received this message on a fatal error:

Fatal error: Uncaught Error: Call to undefined function WC() in /home2/smellgood/public_html/wp-content/plugins/woocommerce-gateway-amazon-payments-advanced/includes/class-wc-amazon-payments-advanced-api.php:171 Stack trace: #0 /home2/smellgood/public_html/wp-content/plugins/woocommerce-gateway-amazon-payments-advanced/includes/class-wc-amazon-payments-advanced-api.php(358): WC_Amazon_Payments_Advanced_API::get_settings() #1 /home2/smellgood/public_html/wp-content/plugins/woocommerce-gateway-amazon-payments-advanced/includes/class-wc-amazon-payments-advanced-api.php(324): WC_Amazon_Payments_Advanced_API::get_region() #2 /home2/smellgood/public_html/wp-content/plugins/woocommerce-gateway-amazon-payments-advanced/woocommerce-gateway-amazon-payments-advanced.php(1375): WC_Amazon_Payments_Advanced_API::is_region_supports_shop_currency() #3 /home2/smellgood/public_html/wp-content/plugins/woocommerce-gateway-amazon-payments-advanced/woocommerce-gateway-amazon-payments-advanced.php(1277): WC_Amazon_Payments_Advanced->get_admin_n in /home2/smellgood/public_html/wp-content/plugins/woocommerce-gateway-amazon-payments-advanced/includes/class-wc-amazon-payments-advanced-api.php on line 171

Our host had to disable all plugins and change to a default theme to get us access to the dashboard again. Changing back to your theme caused another error upon re-enabling Amazon Pay for Woocommerce.

Woocommerce had this to say:
It sounds like a conflict between Amazon Pay extension and your theme occurred, and it was only resolved after switching your site to a default theme.

We do not test our extensions with all other plugins and themes out there since that would be too much to take on. If your site works after re-enabling your theme but crashes again after re-enabling Amazon Pay (with all other plugins except for WooCommerce disabled) – you may want to reach out to the support team of your theme and let them know about this incompatibility.