Start a process, go to task but the form is not shown


I installed the open source version of Flowable.
I defined a process that I included in an app that I published. Now, using Flowable task, I would like to go through the process just as I have achieved to do using the trial enterprise version.

I carefully created a form, provided a valid form key to it, copied and pasted it in the form key field of the desired user task of my process (thus the form key can only be correct, plus I naturally double checked it).
Everything has been saved, so the form and the process are not blank.

When I then go to Flowable task to start the process, the first form is assigned to me, the admin, so it looks fine. However, the form appears blank unlike the provided screenshots from the tutorial I followed (Instant gratification with Flowable 6 blog article).

(It is not the first time that some features don’t appear while they should, such as the claim button that is absent, or the checkbox to define a sequence flow as default flow. I think it is another issue of this type, with the difference that I cannot work around this one).

Here is a screenshot of what I mean by “blank form”:

Thank you a lot in advance

Best regards