Kaldewei Superplan shower tray wobbles, makes noises - help!

Dear forum participants,
I hope someone can help me. I urgently need help from a professional.

Yesterday, I stood for the first time on my new Kaldewei Superplan shower tray 100 x 120 x 2.5 cm.
Installed myself with a friend on a shower tray foot frame FR 5300. Aligned exactly to the millimeter according to the spirit level ... I was very much looking forward to it.
Before that, a plumbing company was involved; after 3 attempts, they did not manage to set up the shower tray correctly, so I did it myself now.
Not least because I no longer want to ask the plumbing company for reworking – I get along wonderfully with the plumber, he has always helped me well and quickly with heating matters... only with the shower tray it just didn’t work out quite right.

Now I stand on it and hear that the outer corner makes noises (creaking?) and wobbles up and down a bit (max 1-2 mm)..?? At the other corners there are no problems.
Luckily, I have not tiled yet, only filled the screed around the shower tray.
Under the shower tray it is hollow, except for a carton approximately in the middle (about 35x35 cm), which the plumber filled with foam.

What can be done now to stop the creaking and wobbling?
How can I find a professional in/around Hannover who has experience with installing Kaldewei Superplan shower trays?

Can someone help me?

Thanks in advance.

Hello there,
the problem with acrylic bathtubs is that they are unstable in themselves.
I would take the tub out again and fasten it to the wall with wall brackets; there should actually have been holders included!

Regards
Mempner

Hi Mempner! This tub is not made of acrylic, but of steel!!! However, only 3.5 mm thick. With dimensions of 100 x 120 cm, that's not much at all.... It is really extremely unstable... Today we placed the tub on [Itongsteine] and [Flex Fliesenkleber]... Tomorrow I will see what has become of it....