I am in a situation: I applied for iOS developer, but then the employer sent me an email says:
Thanks for apply for PHP position. Do you have time for an interview...blah.
What should I response in this situation? Are they testing me?
It's probably just a honest mistake - so tell them you applied for the iOS position.
You really have no alternative; if you don't tell them, do you plan attempting to successfully handle a PHP interview?
Regardless of what happens, they WILL find out that a mistake was made - and it will reflect badly on you not correcting it as soon as possible.
I'm not sure what "applying" and "interviews" have to do with freelancing.... but....
Realize that most people in charge of the first round of hiring choices (Human relations officers/HR) have no idea what the actual skills for a position are. They are merely reading off of a piece of paper or email. The HR department weeds out the completely undesirable candidates, then the interviews involve someone that knows the skills you'll need.
I'd just reply back...
I was seeking the position of an iOS developer. I was not applying for a PHP development position.
I would love an opportunity to interview. However, I'd hate to waste your time if I've mistakenly applied for the incorrect position.
I'm happy to schedule an interview if you are seeking an iOS developer.
Or something along those lines. Don't interview for a position you aren't qualified for, or you don't even want. Clarify the mistake first.