Unable to change Paper Size for printer

I’m trying to print on to a 4x4 card (but UK here so it’s all put in in millimetres). I’ve customised the paper size on my printer okay. I’ve set up the page size on my document just fine. But when I got to print and choose page size, the size needed does not appear and I am unable to insert a custom size, see pic.

Would love some help please!

For printer questions you should always include OS version, LO version, printer model, and how it is connected.

I tried setting a 100 x 100 mm on my Brother MFC-6945dw and my HP 9010 but neither would accept a height less than 127mm due to printer constraints as confirmed by the manual/paper specifications. What is minimum paper height for your printer?

Looking at the number of User Defined sizes it is obvious that LO can use them. If you printer can print a height of 100mm then my guess is that restarting LO will pick up the new size from the printer driver.