What is the expiation for failing to fulfill a vow to pray two rak'ahs daily after Maghrib prayer, which I vowed, and is it permissible to abandon the vow entirely?

Fulfilling a vow (nadhr) is obligatory and emphasized; it is one of the characteristics of believers. Therefore, whoever vows to obey Allah the Almighty must fulfill his vow, and it is not permissible to abandon it except with an excuse. If the one who made the vow is unable to fulfill it for a day or days, or abandons it without an excuse, he must make it up and is sinful for abandoning it. Expiation (kaffarah) is not required of him unless his inability is not expected to cease, in which case he expiates with an oath expiation (kaffarat yamin).

Many scholars disliked making vows because they do not avert anything, but rather extract from the stingy. Some also disliked repeated vows due to the potential hardship, boredom, and failure to fulfill them that they might lead to.