Once I receive John’s approval, I will have your request processed...

Could someone tell me why the following sentence is wrong?

Once I received John’s approval, I will have your request processed

The tenses don’t match. You can say:

“Once I have received John’s approval, I will have your request processed.”
“Once I receive John’s approval, I will have your request processed.”

So if I have a past simple in the subordinate I can’t have a future in the main sentence therefore I should go with a past tense . Is this what you meant?

I think you may have muddled up the words of your question? It’s not impossible to have the structure that I think you are asking about; for example, “Although I received John’s approval last week, I will not be processing your request.” However, I can’t think of any examples that work with “once”.