Extra fees plugin – weird failure

I’m trying to debug a really weird failure with WooCommerce, WooSubscriptions, and thedotstore’s Extra Fees plugin. Here’s what I know:

We have a number of “members”, whose memberships are handled as subscriptions within Woo Subscriptions. We’re trying to add a customized convenience fee for members who pay their monthly membership fee, but only if they’re not using ACH as their payment method. Extra Fees seemed perfect for this, so we installed it and set up the necessary rule. Problem: it works fine on new memberships, but automatic membership renewals are not getting charged the convenience fee.

I’ve been in contact with thedotstore’s support team and they can’t reproduce the problem. That suggests it has something to do with our custom code. Next step is to isolate the problem code — but how do I do that? Either the automatic-renewal code is doing something it shouldn’t that kills the extra fee, or it’s not doing something it should, so the extra fee never gets added. Either way, where do I start? I’ve looked at specific action and filter calls within our plugin code, and gotten nowhere. It all looks like simple and vanilla stuff. How do I tell where, or even if, this code is interacting badly with code in another plugin multiple levels up or down in the call stack?

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