It's softer than saying "El importe de la factura tiene que ser de solo 12 euros." That last example sounds like an order, but if you use the subjunctive, it sounds softer. Subjunctive has that other use, you can make requests sound softer with it (apart from its regular use: would, might, may).
The Language Level symbol shows a user's proficiency in the languages they're interested in. Setting your Language Level helps other users provide you with answers that aren't too complex or too simple.
Has difficulty understanding even short answers in this language.
Can ask simple questions and can understand simple answers.
Can ask all types of general questions and can understand longer answers.
Can understand long, complex answers.
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