What part of speech is for?
For is typically a preposition when determining its part of speech (e.g., “Is this coffee for me?”).
However, “for” can also function as a coordinating conjunction meaning “because” (e.g., “I accepted, for it was a fair offer”).
Have you tried QuillBot’s free Grammar Checker? It will help you to pick up errors with the preposition “for” in your writing.