Email is the only channel
Write to hello@yeargroupmaths.com. There is no contact form on this site, because a form would mean storing what you type on a server, and the rest of the site deliberately avoids that.
The address is read by the person who builds and checks the sheets. It is not a ticket queue and there is no automated reply. Most messages get an answer within a few working days, and messages about a wrong answer on a sheet are dealt with first.
Reporting a wrong answer or a broken sheet
Include the page address, the question number and what you expected. If the problem is on a ready-made PDF, the file name is enough: for example column-addition-year-4.pdf. If it came from the generator, say which year, topic, question count and difficulty were selected, because those four settings decide which question set is built.
A screenshot is welcome but not required. What matters most is the question itself, so the same seed can be rebuilt and checked against the engine.
Suggestions and requests
Requests for a new topic are read, but the site keeps to calculation only, so fractions, shape and problem solving are out of scope by design rather than by oversight. Requests for a different page size are also declined: the layouts are built to A4 and are not tested on other paper sizes.
If you are a teacher who wants a particular question count or difficulty for a year group, say which year and what you would change. Settings that already exist can be adjusted in a minute; new settings need enough demand to be worth the extra controls on the page.