Checking if User has access to an account

This might be simple but I can't figure it out.

My users can have access to one or many accounts. I have a reference field (list) on the User record called accounts. As the user accesses any apis in Xano, I want to first check if the inputted account_id is in his account list.

I tried using preconditions with a Contains or In filter and both gave me errors because this field is an array.

thanks for the help.