What salary are you expecting, and how do you respond when the offer is lower than you hoped?
Suggested answer
The interviewer wants to know whether you prepared, whether you understand your own value, and whether you can talk about salary calmly, without dodging the subject and without making unreasonable demands.
Before you answer, you need to do your homework. If the job ad already states a salary range, that is the best data you can get: you know the range the company is willing to pay. If it doesn't, look at common levels for your role, seniority and location in salary reports and similar job ads. Companies usually build pay in ranges and bands, so there is a ceiling the recruiter can't go above.
When you are asked, give a range with a basis, tied to what you bring (projects, tests, skills that match the requirements), instead of a bare number or a personal reason like rent. If you don't want to name a number yet, you can ask for the salary range of the position first and then answer within it.
When you get an offer that is lower than you hoped, don't accept or reject it on the call. Say thank you, say clearly that you are interested, and ask for the offer in writing and a day or two to think. Read carefully items such as the base salary, the percentage of salary during probation, the end date of probation, the salary that insurance contributions are based on, bonuses and the date of the next salary review, then reply by email, politely, with a specific proposal and your reasons. In Vietnam, the probation salary must be at least 85% of the salary for that job under the 2019 Labor Code.
If the company can't raise the salary, you can ask about other things such as a salary review date in writing, a learning plan or the number of work-from-home days.
Bonus points: mention that comparing the options by total first-year income shows which items are worth asking for, and that polite negotiation is usually a normal part of hiring.