I am following the Marketplace Guide.
I have installed the q2-marketplace module, run create_marketplace_product, and now my SSO extension is inheriting from Q2MarketplaceMixin.

When I sign in as the "retail0" user and run my SSO extension from the Services menu, I now get the following error:

"Your subscription is not valid for this product. Please contact your administrator."

which would seem to be expected in the absence of a subscription being in place for "retail0".

(I also see the following in the log: "Failed to find value for customer key. Verify that Marketplace Store is installed and configured correctly."
I'm not sure whether that is a normal artifact of not finding a subscription, or whether I have failed to do some other required configuration to do Marketplace dev/testing beyond what is mentioned in the Marketplace Guide.)

Now, I want to subscribe the user "retail0" to my marketplace product.

How do I do that?

I thought I could use "q2 markeplace invoke_subscribe" but it seems to use some canned test payload.