Cross-product API calls


we are developing a connect app for Confluence. But we are struggling at one feature:
The user can create a new space with one of our features. We want to create a corresponding project in Jira at the same time. The creation of the space is done in our backend. We have tried to find a solution based on the recent documentation, but we are very unsure what the best way is. The app we are developing should be a paid app.

We evaluate the idea to create a Confluence and a Jira App, but we are very unsure how the communication between both app should be. The JWT from the one App isn’t valid on the other app, right?

Read about forge, where I can make calls for different products: How to Build a Cross-product Forge App for Jira and Confluence - Atlassian Developer Blog

But the marketplace guidelines mentioned:

Note, Forge apps listed on the Marketplace aren’t able to make API calls across different products and instances/installations.

My question is, how is the recommend way to solve this issue. Are there any code samples?

Thanks in advance