[User Testing] A11Y user testing sessions

Hey there -

I am a senior product designer at Remesh <http://www.remesh.ai>, looking to
improve the accessibility of our participant experience. I was wondering if
folks here can direct me to services or companies which can help us with
testing the experience with real users. My team has been owning this
project but we are trying to test our work and the improvement we
are making with different people and different assistive technologies.

Also if you have any recommendations on messaging applications that are
accessible so we can look at some of their work, that would be great too.
Thank you so much!

Cheers,
Amr