Sorry, missed your post. Are both plans exclusive and under the same parent plan or are top level plans? Have you considered using conditions under the workflow tab for the $10 plan to hide if the $30 plan is active?

No, you did not miss my post, you said you relayed it to Beat, but he never got back to me.

Yes I realized that after replying, sorry.

No, I did not consider using the conditions. I thought it would work with the setting. Do you advice to better use a condition?

Yes, I suggest using conditions. That parameter has never worked as it is worded as far as I'm aware and am unsure what its future usage will be in that regard, but conditions will basically achieve the same goal and confirmed working. The below condition should work fine on your $10 plan.

First static condition: This condition must be met to allow upgrades:
Any of the following plans subscriptions: select your $30 plan here
Must be in state: select everything except Active and Not Relevant

Dynamic Conditions (with Javascript animations): These conditions must be met to show this plan dynamically as upgrade:
None of the following plans can also be selected: select your $30 plan here

If you've any issues getting this working please PM me super administrator login credentials and will take a look.