I think that is true, but as @Kiragigi has over 300, I think it's going to be a permissions issue. This seems to be a problem for a lot of members. I'm going to tag @Cicada@dancecats and @Ksnuggles -- in hopes they know how to fix this.
There is a compatibility issue with Tapatalk from what I have been told. We are looking into it. Try to post off of a computer or device not using tapatalk and let me know if you still have the problem.
What @Ksnuggles said is accurate and it bears repeating. We have a known compatibility issue when members attempt to create threads in the marketplace using Tapatalk. If it can be fixed, @Cicada will have to do it.
In the meantime, the best (temporary, we hope) workaround is what @maiarebecca suggests: create the thread/message using the mobile device's browser (or a laptop/desktop) and then add the photos in the subsequent post(s) via Tapatalk.