Find the part of the given sentence that has an error in it.
I think I should have my money back once I didn’t have what was promised in the brochure.

We use since, not once, to introduce a reason:
কারণ বুঝাতে since বসে, once নয়।

অতএব সঠিক বাক্য: I think I should have my money back since I didn’t have what was promised in the brochure.
Not: I think I should have my money back once I didn’t have what was promised in the brochure.

Source: Cambridge Dictionary