Tube in a tubeless tyre?

I'm getting a tube fitted "at my own risk" because of the "ribs inside the tubeless tyre" reason above, by an independant, as I said,
"The cut is about 10mm long on the outer layer only and the actual hole must just be a pin hole as it only bubbles really slowly with soapy water, it was a b****r to find. There is no bulging or distortion around it."
So ther's no cords showing in fact there are bigger deeper cuts/scratches elsewhere and on other tyres that are not leaking.
Personally if I'd had access to a tyre changer machine I'd have tried a puncture repair patch on the inside as the hole is so small.

Sometimes with inner tubes the tyre can spin on the rim a little and rip the valve out as specially with low air pressure.

I have tubes in my tubeless Diamond Backs .. I go to ATS (as KwikFit dont do tubes) .. cost about £20 fitted.