Another one of vs for question, here for would be the right choice, because its use denotes the function of purpose as I think it's the case here, right ?
When customers complaint of an error scenario.
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In normal text, the most frequent prepositions to follow complain is either of or about, with about more common in modern usage. Here’s an OED citation of each version:
The OED says that complain for is obsolete. It meant to lament. Several other possible prepositions now rarely seen occur historically, but have now all become obsolete, or at most, poetic.
First off, you need to learn the difference between "complain" (verb) and "complaint" (noun).
As a verb, this is the paradigm of "complain":
So "complaint" can't be made to act like a verb.
You could change your sentence fragment this way:
Either this or just change the verb to "complain."
About the preposition, the pattern we normally use is:
"Of" is also possible but not "for."