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I am wondering if it is ok to apply for multiple entry visa by just mentioning that I want to travel later in the year or can it lead to rejection if consulate just wants to give single entry visa?
It should certainly be OK to ask but merely βwantingβ to travel again is not necessarily enough. Ideally, you would demonstrate a need to travel regularly, for example because your job requires it. Travel history does help, of course.
Beyond that, there are a bunch of rules and principles on when issuing a multiple-entry visa is appropriate and for how long but those are really just indications; consulates basically do what they want and minimising fees and hassle for the applicants is not always their priority.
The good news is that if the consulate does not want to issue a multiple-entry visa, they don't have to refuse your application, they can simply issue a single entry visa instead, simply checking the box really shouldn't hurt your application.