Prompted by this thread, I've just set up my first UK campaign - going through the KDP dashboard. I was only allowed to do a sponsored product ad, and no ability to add text. (This might be standard for sponsored product ads - I don't do a huge amount of advertising.)
I've tried and stopped!
Thought I'd ask you, or anyone else who has set it up, how straight forward you found it.
I tried clicking the link on the KDP dashboard and on the next page I got the message -
You will need permission to access this page (Yes, it was in red, very dramatic), and then something about contacting my administrator

, I suppose that would be me

I tried clicking on the other link it gives on the KDP page and that took me to seller central...I had a look and clicked out of there, tried that before

. So...
...anyhow...checked out the help page and...
I found that to set it up you go through the bookshelf and then click the market place to create your ad. (helpful that help page

)
So. Like you I could only do a sponsored ad, so I carried on and the first thing I saw was...
You cannot launch a campaign due to your payment method...You can only set up a draft of your new campaign.
So I clicked the link to put this right and saw it already has my card details, but now it wants me to enter my home address and there was something about VAT...WHY? They have my address already, and as for vat, ummm!
I was hoping I could just click on the card and set it to use as payment but no...It want's me to enter the details it already has on .com.
I did save a draft campaign, but when I went back, to maybe have a second go at setting the ad up (I did however give up again, why I'm here) I couldn't find the draft campaign, no idea where that is!
So...That's as far as I've got

Thanks for any help/advise.