As you know, Izad is an old Persian name with Zoroastrian roots. Today, it roughly means "God".

https://fa.wiktionary.org/wiki/ایزد

The word "مهرآفرین" means "آفریننده مهر" (like in Sa'adi's Boustan when it starts with به نام خداوند جان‌آفرین. The word "جان‌آفرین" means "آفریننده جان" which translates to "the Creator [of life]).

As a result, I suggest the translation above.

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Note added at 7 hrs (2022-10-06 13:20:48 GMT)
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Unless your text is of Zoroastrian, "mehr" cannot mean "the sun" in your context.

Yes, one of the definitions of "مهر" is "the sun". In fact, "مهر" is a Zoroastrian god who is "رب النوع آفتاب" (the creator of the sun) (according to فرهنگ فارسی عمید, p. 995).

But it's awkward to say that "ایزد مهرآفرین" in your context refers to "مهر" himself, i.e. the god who has created the sun because of the belief behind it. So, if your text is of Zoroastrian roots, or the writer is Zoroastrian himself/herself, then you might go with "the creator of the sun" or "the Sun-Creating". Otherwise, I believe it's just a literary way to say "In the Name of God" to add to the rhetorical aspects of the text.