Beginner question: I don’t understand where to set the budget in LinkedIn Ads

I need to create a campaign on LinkedIn, but I’m not completely sure at which level the budget should be defined.

I have a daily budget of €15, meaning the campaign should spend around €15 per day, with no specific end date (not negotiable, because it's no mine).

The issue is that when I tried to set this budget at the first level (campaign group), the platform wouldn’t allow it. It said that the budget was too low. In addition, it wouldn’t let me set a lifetime budget without specifying both a start date and an end date.

To move forward, I ended up doing the following: At the campaign group level, I set: Dates: March 6 → April 6 Lifetime budget: €465

This amount comes from the client’s desired daily budget: €15 × 31 days = €465

Then the platform also asked me to define a budget at the campaign level (second level).

But I need to do this: 1 Campaign group (leads gen) 1 campaign with form Daily budget: €15 3 ads: 1 single image 1 carousel 1 video

This is where my confusion starts. I don’t really understand how the budget is actually distributed between the ads, nor why the platform requires a budget both at the campaign group level and at the campaign level.

At the moment, I’m not sure which level the budget should actually be set at, how the spend distribution works, or whether my setup is correct.

Also, ideally the campaign should not have an end date, since the client simply wants it to run with a daily budget of €15. However, LinkedIn doesn’t seem to allow me to do that when I try to define the budget at the campaign group level.

So right now, I’m honestly not sure where the budget should actually be set in this structure.

Thanks in advance for any advice, I really appreciate it!