In Turkish, the sentences "Arkandayım." or "Yanındayım" also mean "I support you". So do "I am behind you" or "I am at you" have such a meaning in English?
In addition, i do not understand the sentence "I am at you." When the system asks for "Benim yanımdasın", i wrote "You are at me." but it was wrong. Can you explain why? Thanks in advance.
Why is, "I have your back" not accepted?
Personally, I only rarely say "I got your back"... On the occasion that I do, I'm more likely to say "I've got your back"
Usually, I will say "I have your back" or "I'll have your back".
They all mean basically the same thing in American English... at least in the regions I've lived in.
There are two genitive case markers one is added to possessor(sen) and other to the possessum(arka). As you did sen takes -in however arka takes -n here. To help you to understand, here is a literal translation:
arka-m (my behind(region behind someone))
arka-n (your behind)
arka-sı (her/his/its behind)
And the locative marker here is -da instead of -de due to vowel harmony. Same goes for -im (The suitable marker here is -ım).
So it becomes 'Ben sen-in(possessor genitive case marker) arka-n(possessum gentive case marker)-da(locative case marker)-y(buffer letter)-ım(first person marker).'
Lucaturilli's answer is very good, but it may help you even further that when he labels the suffix "ım" as the "first person marker," he is referring to what some call "the predicative marker" or what we learned back on tree branch #8 -- To be:
Hope that helps.