Client won't pay-didn't like the work advise please

Hello. Any advice welcome please.

I have been a fashion designer for over 10 years so have experience. I worked on a project for a client. There was a lot of communication throughout the project. He agreed the times and made many amends to the design throughout the project.
Once the design was final I forwarded the invoice and design to him as per agreement. Unfortunately this time I didn't agree a contract or deposit- my bad.
Now he refuses to pay me because he doesn't understand the technical
Spec and explains his factory doesn't understand it either.
However I know from experience it is perfectly fit for a fashion factory to understand.
And I also offered to re do the whole spec at my cost in order to finish the project.....but he still refuses saying the work isn't good enough.
Advice please.
Shall I go straight to small claims?
TIA