What form I need to register my interest to the second home

My ex-husband is currently undergoing an (IVA), and we are still in the process of getting a divorce. He has a second property that is solely in his name, which is currently on the market for sale. What form should I fill out to protect my half share, considering I paid half of the deposit, mortgage, and maintenance fees?

Additionally, could you please let me know the application fee? Thank you.

Man Yi Rita Ke - it's legal advice you need here as to what interest you have and how best to protect it as appropriate
Whilst our PG 19 explains how third party interests might be protected we can't give you legal advice - Practice guide 19: notices, restrictions and the protection of third-party interests in the register - GOV.UK

Land registration is complex, designed to protect legal and financial interests in property. There can be significant consequences for any error. Please consider seeking legal representation.