Unable to use commercial software to submit to HMRc

I am non resident landlord from Hong Kong . I have UTR from HMRC and when I submitted through one of the commercial software , it didn’t get through to HMRC and I couldn’t get refund from the vendor as they say they are not responsible for HMRC side of things . How do I know what error I made ?

Hi msm123 yukkie,

If you are unable to get help from the vendor you will either need to use another vendor or complete a paper tax return.

Thank you.