ken w

Hi, I started getting rental income during the tax year 23-24, and I plan to do a self-assessment to report my rental income. Before 23-24, I did not have rental income and my employer pays tax for me, so I did not need to do anything. However, I started preparing it this year and I found that there is a deadline of Oct 5 to register for self assessment. I tried to still regsiter for self assessment through the government gateway and online form, but I got an email reply saying that my information is not complete. The form is very simple, I just put in the information related to rental income and filled all the lines that are compulsory. I don't think that I missed anything or can provide more information. I submitted the registration by completing the form and double check again, but I think it is still the same information. I am waiting for the reply. Do I get this email because that my information is incomplete or because I missed the deadline? Shall I call HMRC to ask and hopefully get registration done online? If I don't get the registration approved and submit my self-assessment before Jan 31 deadline, I think I can still amend my tax return for previous year. I can report my rent income afterwards by amending the previous year's income, is that correct? Will there be a fine for this? Thanks!