Technical requirements are often ambiguous when written as free text, the way someone would speak them, because as you have discovered the free text fails to capture where the linguistic stress would be that disambiguates in speech.
Instead, I suggest using a format that is more suited to text.
I would recommend a table. Email the customer back with your interpretation of the requirements, with a column for outcome and a column for value. Ask them to check and sign off on the table, or to correct the table where it is wrong.
Cheers yeah, that is standard usually. I was just having a whinge rather than asking for a solution. In this case the customer was trying to preempt having to complete a change request form (similar to what you’ve described) and get the relevant sign off etc, and had emailed over a “minor alteration” to an existing request, for which they should know better at this stage of the project.
Completely agree, requirements are key and often badly defined due to the customers' lack of knowledge of the intricacies of the system. You are correct to ask for clarity or it could come back to bite you later on.
I've just had a spec through from a BA which consists entirely of screenshots of an existing system with no technical definitition of any of the requested fields so relate to this right now.