It does not seem to work in the merchandise plan. I tried the standard substitution [cb_field] and [cb:userfield field="cb_field" /] but both do not work. The field is correctly editable on the profile but not on the merchandise plan area. Any idea ?

Don't understand what you're asking. You want to render the ajax editable version of a field in your merchandise plan description? I'm not sure you can do that, but you can try. The below would be proper syntax for it.

[cb:userfield field="FIELD_NAME" formatting="div" /]

Output defaults to html and reason defaults to profile so all you should need to do is ensure it outputs as div format. I've no idea if this is going to work though. I thought you meant have the field on their profile ajax editable.

Would it be possible to have it as a simple listing in a tab ?

I don't think so. It's all calculated from several different database tables. Normally you'd just use CB Query Field, but you won't be able to do any of the calculations needed. Maybe you can use an iframe with the invoice page URL and &tmpl=component appended to the URL. You'd need to allow iframes within CB > Configuration > User Profile though (have to whitelist it).

No this syntax does not work in merchandise plans.

We need it for the user to change values in the merchandise plan before submitting it so that we can use these values in the emails sent with the integration.

You'll have to ask for this information at registration or profile edit then. There's currently no way to ask for them to complete a field or anything of the sort during purchase.

Thanks we'll try, it is important for customers to track their purchases independently of invoicing. This is something to add in next version maybe ?

Probably not as we already have a dedicated page for invoice list display, but maybe in a future release it can be a tab or a field.